mi. SE Sheffield, Pecos County; TU 14453 (7), 14462 (2), 15415, 15423,

15586, Pecos River near jct. with Independence Creek; USNM 104240, Pecos River "near" Dryden. _Val Verde_: TTC 113, Pecos River. _Webb_: TNHC 19788, 42 mi. NW Laredo; USNM 109078-79, Laredo. _Zapata_: UI 19332, "near" Zapata. _County unknown_: MCZ 1628, USNM 7635-36, 7854; USNM 7637-38, Río Bravo (= Río Grande).

CHIHUAHUA: KU 51173, 8 mi. S, 16 mi. W Ojinaga; KU 51174-86, 1 mi. NW Ojinaga; KU 51187-201, Río Conchos at mouth of Río San Pedro near Meoquí; UI 43508-09, Río Florida, La Cruz.

COAHUILA: CNHM 26054, Sta. Helena Canyon of Río Grande; CNHM 28846, "near" Músquis; CNHM 55657, Río Alamos, Rcho. de la Gacha; CNHM 47366, Sierra de Santa Rosa, La Palma; CNHM 47367, 55661, Cuatro Ciénegas; CNHM 55658-60, Rcho. de los Borregos near Juarez; KU 33523, La Presa Don Martín; KU 39991, 39993, 8 mi. N, 2 mi. W Piedras Negras; KU 39992, 2 mi. W Jiménez; KU 46907, 16 km. S Cuatro Ciénegas; KU 46913-16, 10 km. S Cuatro Ciénegas; KU 53752-54, Río Mesquites, 8 mi. W Nadadores; KU 53757, 8.5 mi. SW Cuatro Ciénegas; MSU 905-06, Río Sabinas, 1 mi. E Sabinas.

NUEVO LEON: CNHM 1874, 2191, Rodriguez; UMMZ 69411, Río Conchos, 9 mi. N Linares.

TAMAULIPAS: CM 3037, Nuevo Laredo. UMMZ 7614-20, 7622-25, 7628, 7630, 7632-33, Matamoros; UMMZ 69412, Río Purificación, N of Ciudad Victoria.

NO DATA: MCZ 1629 (2), NHB 1032.

_Records in the literature._--ARIZONA: _Greenlee_: Gila River, Duncan (Miller, 1946:46); "near" Sheldon (Dill, 1944:180). _Mohave_: Pierce's Ferry just below lower end of Grand Canyon (Cowles and Bogert, 1936:42); 1.5 mi. upstream (Virgin River) from Mesquite, Clarke County, Nevada (Hardy and Lamoreaux, 1945:168); Lake Havasu on Colorado River (Dill, 1944:180). _Yuma_: Colorado River at Headgate Rock Dam (Dill, _op. cit._:179).

CALIFORNIA: _Imperial_: California Lakes (Cowles and Bogert, 1936:42); Palo Verde; Colorado River at Laguna Dam (Dill, 1944:180).

NEVADA: _Clark_: observed just north of Black Canyon (Cowles and Bogert, _loc. cit._); Colorado River, 6 mi. N California line (Linsdale, 1940:255).

NEW MEXICO: _Chaves_: Bitter Lakes Wildlife Refuge, 12 mi. NE Roswell (Bundy, 1951:314). _Dona Ana_: Río Grande near Mesilla Dam (Little and Keller, 1937:221).

TEXAS: _Brewster_: Río Grande at Castolon (Minton, 1959:38). _Val Verde_: mouth of Devil's River (Brown, 1950:250).

BAJA CALIFORNIA: Colorado River delta, 7 mi. E Cerro Prieto; Imperial Irrigation District, Alamo Canal, 15 mi. S Internat'l Boundary and Salfatana Canal, 1 mi. N Black Butte (Linsdale and Gressitt, 1937:222).

COAHUILA: San Juan (Schmidt and Owens, 1944:103).

Hitherto, soft-shelled turtles of the species _Trionyx spinifer_ from the southern and southwestern United States having a pattern of white dots on the carapace have been relegated to the subspecies _emoryi_, but my examination of soft-shelled turtles from Texas has indicated that _T. s. emoryi_ as previously conceived, is a composite of three subspecies. It is necessary, therefore, to recognize two new subspecies.

=Trionyx spinifer guadalupensis= new subspecies

Guadalupe Spiny Softshell

Plates 41 and 42

_Holotype._--UMMZ 89926, alcoholic adult male; obtained 15 miles northeast Tilden, McMullen County, Texas (Pl. 41, bottom, left).

_Paratypes._--Forty-two specimens: ANSP 16717 (hatchling), no data; USNM 78515-16 (hatchlings), Colleto Creek, Victoria County, Texas; TU 10143-45, 10148, 10150-59, 10161-65 (adult males), TU 10176, 10833 (immature males), TU 10147, 10149, 10155 (immature females), TU 10160 (adult female), Guadalupe River, 9 miles southeast Kerrville, Kerr County, Texas; UMMZ 89915-21, 89924-27 (adult males), UMMZ 89922-23 (immature females), same locality as holotype; UMMZ 92752 (immature female), San Antonio River, 3 miles west-northwest Goliad, Victoria County, Texas.

_Description of holotype._--Carapace nearly circular, widest at level of posterior border of hypoplastra; margin entire; dorsal surface "sandpapery" to touch; pale rim separated from ground color of carapace by well-defined, blackish line that is wavy and narrowly interrupted posteriorly and anteriorly; pale rim approximately 1.8 times wider posteriorly (5.4 mm.) than laterally (3.0 mm.); pale rim increasingly narrower anteriorly, absent in nuchal region; tubercles in nuchal region low, scarcely elevated, lacking sharp tips; ground color of carapace olive having pattern of whitish spots and small tubercles; most whitish tubercles inconspicuous pinpoints; other small tubercles in center of whitish spots, mostly approximately 2 millimeters in diameter; largest white spot 3.4 millimeters in diameter; most white spots surrounded by blackish ocelli or parts thereof; whitish spots distributed over entire surface of carapace; certain features of bony carapace evident through overlying skin; carapace highest in region of second and third neurals, forming obtuse, gently sloping, vertebral, keel; undersurface of carapace butterscotch yellow, lacking markings; maximum length, 16.5 centimeters; greatest width, 13.5 centimeters.

Plastral surface butterscotch yellow, lacking markings, extending slightly farther forward than carapace; anterior and posterior lobes rounded; anterior lobe slightly truncate; certain features of bony elements of plastron visible through overlying skin; maximum length of plastron, 12.0 centimeters.

Head, extended to posterior level of eyes, terminating in flexible snout; septal ridges projecting into each rounded nostril; jaws closed, each covered by fleshy lips except anteriorly where horny portions exposed; dark triangular mark in front of eyes, base line connecting anterior margins of orbits forming series of dots; pale stripes extending forward from eyes having faint inner, blackish borders; eyelids partly open having blackish dots; pale subocular blotch on right side of head having border of black dots.

Forefeet and hind feet well-webbed having five digits each; each limb having nails on first three digits; each forelimb with four antebrachial scales, three of these having free edge; each hind limb with two horny scales, one smooth on posterodorsal surface and other with free edge on posteroventral surface; pattern toward insertion of forelimbs indistinct.

Tail terminating in flexible point; penis exposed; cloacal opening extending beyond posterior edge of carapace; tail olive above bordered by blackish marks; few black dots laterally on left side.

Undersurface of soft parts of body buff, lacking markings; few dark marks posteriorly on webbing of limbs, encroaching on soles and palms.

_Range._--Southcentral Texas in the drainage systems of the Nueces and Guadalupe-San Antonio rivers; the Colorado River drainage in Texas is inhabited by a population that more closely resembles _guadalupensis_ than _pallidus_. See comments under subsection entitled "Remarks" and Fig. 19.

_Diagnosis._--Juvenal pattern of white dots that are conspicuous on anterior half of carapace, and usually as large as those on posterior half; white dots, sometimes 3 millimeters in diameter, encircled with blackish ocelli in adult males.

_Description._--Plastral length of smallest hatchling, 3.3 centimeters (ANSP 16717); of largest male, 13.5 centimeters (TU 10162); of largest female, 22.0 centimeters (TU 10160).

Hatchlings having white dots on anterior half of carapace; white dots anteriorly nearly as large as those posteriorly, encircled with blackish ocelli, and conspicuous on dark background (ANSP 16717, Pl. 41; USNM 78515-16; Stebbins, 1954:181, Pl. 26B), or smaller than those posteriorly, not encircled with dusky ocelli, and inconspicuous on pale background (TNHC 1446); pale rim of carapace less than four times as wide posteriorly as laterally.

Adult males resembling holotype; size of white tubercles on carapace variable; most, if not all, tubercles surrounded by narrow blackish ocelli, or parts thereof; largest white tubercles or dots in most specimens exceeding one millimeter and in some specimens three millimeters in diameter (TU 10163); white dots often slightly elongate (UMMZ 89917, 89920, 89926; TU 10152, 10145); juvenal pattern of white dots seemingly more contrasting in _guadalupensis_, owing to dark ground color of carapace, than in _pallidus_ or _emoryi_ that have pale brown or tan carapaces; small tubercles along anterior edge of carapace rounded, obtuse, wartlike, never conical; sharp tips often lacking (TU 10153).

Large females often having whitish spots on anterior half of carapace (TU 10160, Pl. 42, upper, right; 10142); carapace dark having ill-defined mottled and blotched pattern; tubercles along anterior edge of carapace low, rounded, rarely equilateral, never conical; small blackish dots rarely on surface of carapace (UMMZ 89923).

Pattern on side of head and snout of little diagnostic value; postocular stripe usually interrupted, but configuration variable, consisting of pale anterior, dark-bordered segment (just behind eye); posterior segment of postocular stripe usually less well-defined and generally blending with adjacent ground color; pale postocular stripe sometimes uninterrupted and dark-bordered throughout its length (TU 10157, 10159, 10176); pattern on dorsal surface of snout variable; pattern usually consisting of uninterrupted dark line (slightly curved anteriorly) connecting anterior margins of orbits (TU 10161, 10164, 10159, 10143), or dark line interrupted (TU 10153, 10154, 10176), absent (TU 10163), or present in addition to dark inner borders of pale stripes that extend anteriorly from eyes (TU 10149, 10162); small, often fine, dark markings, on dorsal surface of limbs, especially forelimbs; ventral surface of plastron and soft parts of body usually whitish, lacking markings; small blackish spots occasionally in region of bridge (TU 10149); dark marks occurring on webbing of limbs and often encroaching on soles and palms.

Ontogenetic variation in PL/HW, mean PL/HW of specimens having plastral lengths 7.0 centimeters or less, 3.83, and exceeding 7.0 centimeters, 5.18; ontogenetic variation in CL/CW, mean CL/CW of specimens having plastron lengths 8.5 centimeters or less, 1.14, and exceeding 8.5 centimeters, 1.22; mean CL/PCW, 2.11; mean HW/SL, 1.38 (including subspecies _pallidus_); mean CL/PL, 1.37.

_Variation._--Two hatchlings (ANSP 13447, Bexar County; TNHC 1446, McMullen County) more closely resemble _pallidus_ than _guadalupensis_.

Some individuals from the Colorado River drainage have features suggesting those that are characteristic of _pallidus_. Large females have obtuse, knoblike somewhat triangular-shaped tubercles along the anterior edge of the carapace, which are never conelike (TU 14439-40, 10187, 16036.1; BCB 6010). The tubercles along the anterior edge of the carapace are more elevated than in turtles from drainage systems west of the Colorado. Whitish spots are usually absent anteriorly on the carapace, but may be evident through the mottled pattern of large females (BCB 6010, plastral length, 19.7 cm.). The pale postocular stripe is usually interrupted, whereas the dark line connecting the anterior margins of the orbits is usually not interrupted; the two characters last mentioned show alliance with _guadalupensis_.

The carapace of hatchlings from the Colorado River is pale having whitish dots, smaller anteriorly than posteriorly, which may be encircled with dusky ocelli (TNHC 20257) or not (ANSP 11889, BCB 5055, SM 3282). Many hatchlings are not distinguishable from _pallidus_ (TCWC 7262, TNHC 4975, SM 4924, 6106). I have not seen hatchlings from the Colorado River that resemble ANSP 16717.

The pattern on the carapace of adult males from the Colorado River drainage resembles that of _guadalupensis_ (Pl. 41, bottom, right) but the whitish dots are usually smaller and may not be encircled with blackish ocelli (BCB 4066, TU 14485). An adult male (TU 14476) from the South Fork of the Llano River has whitish dots three millimeters in diameter and encircled with blackish ocelli (_guadalupensis_), whereas another adult male (USNM 83690) from a tributary of the Colorado, the South Concho River, resembles _pallidus_.

Eight specimens from the San Saba River (TU 14419 [6 specimens], 14439-40), that range in plastral length from 6.8 to 17.0 centimeters are impressive because of the dark brownish coloration on the carapace. The smallest individual, which is also the only male in the series, is paler. The mottled and blotched pattern on the females is therefore not contrasting; the largest females have elevated whitish prominences in the center of the carapace posteriorly. An immature male (UMMZ 70348) from the South Concho River also has a dark brown carapace, and lacks white dots. The dark coloration of the carapace of these specimens recalls the TU series of _T. s. emoryi_ from the Pecos River, Terrell County, Texas.

Color notes taken from a freshly-killed adult female from the Llano River, two miles west Llano (TU 16036.1, Pl. 42), are: pattern on carapace of dark olive or blackish marks that form an irregular reticulum or marbling on a paler background that varies from brownish to buff and has an orange or reddish tinge in some areas; small whitish spots posteriorly; pale rim yellowish, evident only at sides of carapace; dorsal surface of soft parts of body olive-green, becoming paler with yellowish tinge toward insertions of limbs and neck; no contrasting pattern on limbs or neck and head; yellowish on sides of body; ventral surface whitish lacking dark marks, yellowish at region of bridge, axillary region and on neck; chin olive-yellow.

_Comparisons._--_T. s. guadalupensis_ can be distinguished from all other subspecies of _T. spinifer_ in having: (1) large white dots, sometimes three millimeters in diameter, on a dark background usually surrounded with blackish ocelli and conspicuous on the anterior half of the carapace (some as large as those on posterior half) in adult males, and (2) whitish dots on the anterior half of the carapace, in hatchlings, that are often encircled with dark ocelli. _T. s. guadalupensis_ resembles _pallidus_ and _emoryi_ in having white tubercles or dots on the carapace and therein differs from _spinifer_, _hartwegi_ and _asper_. _T. s. guadalupensis_ resembles _pallidus_ but differs from _emoryi_ in having a pale rim that is less than four times wider posteriorly than laterally. _T. s. guadalupensis_ resembles _emoryi_ but differs from _pallidus_, _spinifer_, _hartwegi_ and _asper_ in having along the anterior edge of the carapace tubercles that are flattened or wartlike prominences often lacking sharp tips in adult males; these tubercles are never conical in large females.

_T. s. guadalupensis_ has a wide head, a feature shared with the subspecies _asper_ and _emoryi_, but differs from _emoryi_ in having a wider carapace. _T. s. guadalupensis_ resembles _emoryi_ and _pallidus_ but differs from the other subspecies in having the carapace widest farther posterior than one-half the length of the carapace. The length of snout in _pallidus_ and _guadalupensis_ is shorter than in _spinifer_ and _hartwegi_ but is longer than in _emoryi_. _T. s. guadalupensis_ differs from _asper_ but resembles the other subspecies in having a relatively long plastron.

_Remarks._--Some individuals of _guadalupensis_ have characteristics that are applicable to _emoryi_. TNHC 12352 (Llano River) a hatchling, has conspicuous white dots confined to the posterior third of the carapace; the pale rim, however, is not widened posteriorly. TU 10156 (Guadalupe River) has a conspicuously widened pale rim on the carapace that is approximately 3.4 times wider posteriorly (8.5 mm.) than laterally (2.5 mm.).

_T. s. guadalupensis_ more closely resembles _pallidus_ than _emoryi_. Turtles living in rivers that drain into the Gulf of Mexico east of the Guadalupe-San Antonio river system successively show increasing resemblance to _pallidus_ from west to east.

The expression of intergradation between _guadalupensis_ and _pallidus_ is of a clinal nature that involves parallel changes in the pattern on the snout, side of head, limbs (to a lesser degree), tuberculation along the anterior edge of the carapace, size of whitish tubercles or dots, and the distinctness of the blackish ocelli that surround the whitish dots on the carapace. These characters form a well-marked gradation or cline that extends over a considerable area. There is, however, no continuous environmental gradient because the populations are relatively isolated by occupying adjacent drainage systems. The sharpest break in the gradation of characters mentioned above occurs between the Colorado River and Brazos River drainages. The population of softshells in the Colorado River drainage is actually an intergradient one, but more closely resembles _guadalupensis_, whereas the population in the Brazos River drainage more closely resembles _pallidus_. For convenience the turtles inhabiting the Colorado River drainage are referred to _guadalupensis_ and those in the Brazos River drainage to _pallidus_. Some individuals from farther west than the Colorado River drainage will resemble _pallidus_, and a few individuals from father east than the Brazos River drainage will resemble _guadalupensis_.

The gradation of some of the characters mentioned above terminates in the subspecies _emoryi_. It, however, has characters not found in _pallidus_ or _guadalupensis_, and is more distinct from either of those subspecies than either is from each other; the difference in characters as well as the break in the gradient of characters between _guadalupensis_ in the Nueces River drainage and _emoryi_ in the Río Grande drainage is greater than that between _guadalupensis_ in the Colorado and _pallidus_ in the Brazos River drainages.

I have refrained from designating individuals between these three subspecies (_emoryi_, _guadalupensis_ and _pallidus_) as "intergrades" on the distribution maps, and only mention (in text) those individuals whose characters show a decided tendency toward the adjacent subspecies. For further comments on intergradation see the account of _T. s. pallidus_.

_Specimens examined._--Total 97, as follows: TEXAS: _Bandera_: KU 50834, Hondo Creek, 4 mi. W Bandera; TNHC 797-98, 7 mi. SW Medina. _Bexar_: ANSP 13447, Helotes; MCZ 4587; USNM 10789, 71009, San Antonio. _Borden_: BCB 4066, 7 mi. N Vincent. _Brown_: TNHC 7262, 1 mi. E Brownwood. _Comal_: USNM 7700, New Braunfels. _Dawson_: TNHC 21594-95, 10 mi. E Lamesa. _Frio_: USNM 7747, Río Seco. _Gillespie_: TU 10185, 10187, 10205, Beaver Creek, "near" Doss. _Hays_: AMNH 29950-52, San Marcos. _Kerr_: SM 2553, headwaters Turtle Creek; TU 10142-45, 10147-65, 10176, 10833, Guadalupe River, 9 mi. SE Kerrville. _Kimble_: BCB 5052-55, 6010, 3 mi. SE Telegraph; TU 14476, South Fork Llano River, 1.5 mi. SE Telegraph; TU 14485, Llano River, 10 mi. W Junction. _Lavaca_: SM 2554-55, 2559, 3 mi. NNE Hope. _Llano_: TNHC 12352, TU 16036 (2), Llano River, 2 mi. W Llano. _McMullen_: TNHC 1446, 10 mi. W Simmons, Live Oak County; UMMZ 89915-27, 15 mi. NE Tilden. _Matagorda_: ANSP 11889, Matagorda. _San Saba_: SM 6106; TU 14419 (6), 14439-40, San Saba River, 11 mi. NNW San Saba. _Tom Green_: SM 3282, UMMZ 70348, USNM 83690, South Concho River at Christoval. _Travis_: SM 659-60, 8.5 mi. from mouth of Onion Creek in Colorado River near Austin; SM 4924, Onion Creek; TNHC 4975, Upper Bull Creek; TNHC 20257, Marshall Ford Dam. _Victoria_: CM 3118, Black Bayou; UMMZ 92752, San Antonio River, 3 mi. WSW Goliad; USNM 78515-17, Colleto Creek, Guadalupe River. _County unknown_: ANSP 16717; TNHC 1404.

_Records in the literature._--TEXAS: _Bandera_: 24 mi. WNW Medina (Brown, 1950:250). _Burnet_: Colorado River (Strecker, 1909:8). _Gillespie_: 20 mi. N Harper (Brown, _loc. cit._). _Kendall_: Cibolo Creek at Boerne (Strecker, 1926:8). _Kerr_: Guadalupe River, 3 mi. above Kerrville (TCWC 474, listed in card file). _Mason_: 12 mi. NE Mason (TCWC 3303, listed in card file). _Matagorda_: Bay City (Brown, _loc. cit._). _Real_: (Stejneger, 1944:66). _Wilson_: Cibolo River, 30 or 40 mi. N Sutherland Springs (Strecker, 1935:23).

=Trionyx spinifer pallidus= new subspecies

Pallid Spiny Softshell

Plates 39 and 40

_Holotype._--TU 484, alcoholic adult male; obtained from Lake Caddo, Caddo Parish, Louisiana on June 27, 1947, by Fred R. Cagle and party (Pl. 39, lower, left).

_Paratypes._--Forty-two specimens: TU 481, 490, 678 (hatchlings), TU 381, 472, 488 (immature males), TU 475, 478, 486, 1232, 1291, 10170 (adult males), TU 399, 487 (immature females), TU 469 (adult female), Caddo Lake, Caddo Parish, Louisiana; TU 15818 (immature male), TU 15819 (adult male), Cross Lake, Caddo Parish, Louisiana; TU 1253, 13211 (adult males), TU 13266 (immature female), Sabine River, 8 miles southwest Merryville, Beauregard Parish, Louisiana; TU 13281-82 (adult males), TU 13280, 13265 (immature females), TU 13303-04, 13306 (adult females), Sabine River, 8 miles southwest Negreet, Sabine Parish, Louisiana; SM 2375 (adult male), Wallace Bayou, De Soto Parish, Louisiana; TU 1122 (adult male), Lacassine Refuge, Louisiana; UMMZ 92754 (adult male), 5 miles west Iowa, Calcasieu Parish, Louisiana; KU 40174-76, OU 27297 (adult males), OU 27290 (immature female), Lake Texoma, 2 mi. E Willis, Marshall County, Oklahoma; KU 50832 (hatchling), mouth of Caney Creek, 4 miles southwest Kingston, Marshall County, Oklahoma; CNHM 15474 (immature female), Kiowa County, Oklahoma; KU 2966-67 (immature females), KU 2934, 2947 (adult males), KU 2973 (adult female) Lewisville, Lafayette County, Arkansas.

_Description of holotype._--Carapace circular, widest at level of posterior edge of hyoplastra; margin entire; dorsal surface "sandpapery" to touch; pale rim separated from ground color of carapace by well-defined, slightly ragged, blackish line; pale rim approximately 2.1 times wider posteriorly (4.7 mm.) than it is laterally (2.2 mm.); pale rim increasingly narrower anteriorly, absent in nuchal region; tubercles along anterior edge of carapace triangular with sharp tips becoming flattened and inconspicuous at level of insertions of arms; ground color of carapace brownish having pattern of small whitish tubercles; most whitish tubercles inconspicuous, of pinpoint size, giving surface of carapace "sandpapery" effect; largest white tubercles posteriorly, approximately 1.2 millimeters in diameter; whitish tubercles smaller anteriorly, largest approximately 0.6 millimeters in diameter; whitish tubercles tend to form two parallel lines coincident with longitudinal sutures of neurals posteriorly in center of carapace; certain features of bony carapace evident through overlying skin; carapace highest in region of third and fourth neurals, forming obtuse, gently sloping, vertebral keel; undersurface of rear margin of carapace whitish having pinkish tinge and no markings; maximum length, 16.8 centimeters; greatest width, 14.3 centimeters.

Plastral surface extending slightly farther forward than carapace, whitish having pinkish tinge and no dark markings; anterior and posterior lobes rounded, posterior lobe more acutely; certain features of bony elements of plastron visible through overlying skin; maximum length, 12.2 centimeters.

Head extended, terminating in flexible snout; septal ridges projecting into each rounded nostril; tip of snout darkened; jaws open, each covered by fleshy lips except anteriorly where horny portions exposed; dark triangular mark in front of eyes, base line uninterrupted, slightly curved anteriorly, connecting anterior margins of orbits; eyelids having blackish dots, especially upper, closing eyes; small blackish dots on dorsal surface of head; pale postocular stripe dark-bordered, interrupted; pale portion of stripe traversed by black line; pale subocular blotch margined by broken blackish border; side of head having contrasting blackish marks on pale background; postlabial stripe having lower blackish border on right side of head; chin with ill-defined marks, not contrasting on grayish background; well-defined, ragged black line on side of neck separating dorsal coloration from immaculate ventral coloration; small dark dots on dorsal surface of neck; dorsal surface of head and neck olive or brownish, becoming paler laterally and toward insertion of neck; maximum width of head, 2.1 centimeters.

Forefeet and hind feet well-webbed each having five digits; each limb having nails on first three digits; each forelimb with four antebrachial scales, three of which have free edge; each hind limb with two horny scales, one smooth on posterodorsal surface and other with free edge on posteroventral surface; contrasting pattern of blackish marks, mostly roundish, on pale background of grayish-white.

Tail terminating in flexible point; penis partly exposed; cloacal opening extending beyond posterior edge of carapace; tail having dorsal grayish band flanked by interrupted blackish lines; dark marks encroaching ventrally at tip of tail.

Undersurface of soft parts of body whitish, with pinkish tinge; dark marks lacking on soles, present on webbing and palms; dark marks arranged in linear fashion coincident with digits.

_Range._--Southern Oklahoma, eastern Texas, extreme southwestern Arkansas, and the western half of Louisiana; Red River drainage and rivers that drain into the Gulf of Mexico east of the Brazos River drainage in Texas and west of the Atchafalaya River drainage in Louisiana. The Brazos River drainage is inhabited by a population that more closely resembles _pallidus_ than _guadalupensis_ (see comments under subsection entitled "Remarks"; see map, Fig. 19).

_Diagnosis._--Juvenal pattern of white dots that are usually absent or inconspicuous, but sometimes distinct and small, on anterior third of carapace, and not surrounded with dark ocelli; white dots often absent on posterior half of carapace of hatchlings; white spots, rarely as large as two millimeters in diameter, not encircled with black ocelli on adult males; pale rim of carapace less than four times wider posteriorly than laterally.

_Description._--Plastral length of smallest hatchling, 3.3 centimeters (KU 50832); of largest male, 16.0 centimeters (SM 2375); of largest female, 30.5 centimeters (TU 13213).

Surface of carapace in hatchlings uniform pale brown or tan; small white tubercles absent or inconspicuous on anterior half of carapace, but evident on posterior half of carapace, sometimes well-defined (TU 481), but usually inconspicuous (TU 678, 490); pale rim of carapace less than four times wider posteriorly than laterally.

Adult males resembling description of holotype; small whitish tubercles or dots rarely two millimeters in diameter on posterior half of carapace, smaller and usually inconspicuous on anterior half of carapace (TU 13281, 486); well-defined whitish tubercles occasionally on anterior half of carapace (KU 40174); white tubercles not surrounded with black ocelli; pattern of white dots seemingly less contrasting in _pallidus_ than in _guadalupensis_, owing to pale brown or tan carapace; small tubercles along anterior edge of carapace equilateral or conical having sharp tips.

Large females usually having pale brown carapaces with slightly contrasting, brownish, mottled and blotched, patterns; white prominences often evident posteriorly and anteriorly in middle of carapace and in nuchal region; tubercles along anterior edge of carapace equilateral or conical in shape.

Pattern on side of head and snout variable and of no diagnostic value; postocular stripe uninterrupted having dark borders (UMMZ 92754), or interrupted having pale segment behind eye (TU 13282); other variations in pattern shown on TU 10170 and 15818; pale stripes on snout having dark inner borders that join and form acute angle (TU 381), or lacking dark inner borders and having uninterrupted dark line connecting anterior margins of orbits (TU 13280); other variations in pattern on snout shown on TU 1232, 1291 and 15819; specimens representing illustrations of variation in pattern on snout (Fig. 5 d, e, f) all from same locality, Lewisville, Lafayette County, Arkansas; contrasting pattern on side of head of dark marks on pale background; contrasting pattern of dark marks on dorsal surface of limbs; markings on hind limbs generally larger than those on forelimbs; small or fine markings of some specimens reducing contrast in pattern (TU 478, 488); carapace sometimes having few small blackish dots confined to margin (CNHM 15474, TU 487, 1253, 13266); ventral surface of plastron and soft parts of body whitish and usually lacking dark markings; small blackish marks often occurring on flap of carapace, in region of bridge, or on chin and throat (TU 399, 469, 475, 472, 13281).

Ontogenetic variation in PL/HW, mean PL/HW of specimens having plastral lengths 7.0 centimeters or less, 4.15, and exceeding 7.0 centimeters, 5.32; ontogenetic variation in CL/CW, mean CL/CW of specimens having plastral lengths 8.5 centimeters or less, 1.10, and exceeding 8.5 centimeters, 1.14; mean CL/PCW, 2.12; mean HW/SL, 1.38 (including subspecies _guadalupensis_); mean CL/PL, 1.36.

_Variation._--In 1953, I casually glanced at a hatchling softshell from the Calcasieu River drainage in the private collection of Mr. Wilfred T. Neill; the specimen was considered by Neill (1951:15) as "... an intergradient one (with the _hartwegi-spinifer_ population in the lower Mississippi drainage)." The hatchling does deviate from "typical" _pallidus_ in having darkish flecks posteriorly on the carapace.

I have seen only one adult male (USNM 94457) from the Sabine River drainage (Orange County, Texas) that shows characteristics of _guadalupensis_ (white dots on carapace encircled with small black ocelli); another adult male (USNM 94456) from the same locality resembles _pallidus_. Those two USNM specimens were mentioned by Neill (1951:13) as indicating intergradation with "... the mixed _spinifera-hartwegi-asper_ populations of Louisiana."

Two adult males (SM 2889, Pl. 40, bottom, left, and TCWC 471, Trinity River drainage) have blackish ocelli surrounding the white dots on the posterior part of the carapace; two large females (TU 14402, Pl. 40, bottom, right, plastral length, 17.5 cm., and TU 14417 plastral length, 21.3 cm., both from the Trinity River) have contrasting mottled and blotched patterns with white dots visible on the carapace. These turtles show alliance with _guadalupensis_.

Some individuals from the Brazos River drainage have features suggesting those that are characteristic of _guadalupensis_. Hatchlings may have large white dots on the anterior half of the carapace (USNM 55601). Adult males may have dusky ocelli surrounding the white dots on the carapace (TU 14169, 14559.1, 14559.2). The whitish dots, rarely as large as two millimeters, are never so large as in _guadalupensis_ (three mm. in diameter), and are usually smaller anteriorly than posteriorly; TU 14169 has white dots approximately the same size (1.2 mm.) on the anterior half as on the posterior half of the carapace. The tubercles on adult males are equilateral or subconical, usually having sharp tips (TU 14348, 14559.1, 14559.2); the tubercles on large females are subconical, resembling the end of a bullet, and, in both sexes the tubercles are less conical than those on specimens of _pallidus_ from farther east.

Three specimens from the Brazos River drainage are particularly impressive in their alliance with _guadalupensis_. SM 2556, an adult male, has large white dots that are encircled with black ocelli on the posterior half of the carapace, but lacks white dots on the anterior half. TNHC 14068, a hatchling, has small black dots interspersed with the larger white dots posteriorly. CNHM 46289 has large white spots on the carapace that are surrounded with two to four black dots; scattered black dots also intermix with white spots on the surface of the carapace (less extensive anteriorly).

Color notes taken from a freshly-killed adult male (KU 47121) from the Brazos River, seven miles below Whitney Dam, Bosque-Hill county line, Texas, are: Carapace pale brown or tan bordered by black line, having pale lemon yellow rim; yellowish-cream spots on carapace faintly surrounded with black stippling; dorsal surface of soft parts of body olive having black marks and patches of grayish; webbing on limbs having golden or yellowish hue, brighter distally; interorbital region brown; black-bordered, postocular stripe orange-cream; snout and side of head olive having pale areas of orange-cream; iris cream having black stripe; yellowish at juncture of dark dorsal and pale ventral coloration with orangish tinge on forelimbs and head; tail pale brown or tan, flanked by black borders that suffuse laterally into lemon-yellow; undersurface whitish, pale yellow on neck, bluish-gray on throat.

_Comparisons._--_T. s. pallidus_ most closely resembles _T. s. guadalupensis_, but can be distinguished from that subspecies in having small white tubercles, rarely two millimeters in diameter, on a pale background, that are not surrounded by blackish ocelli, and are usually absent, or not conspicuous on the anterior third of the carapace in adult males; also there are usually no conspicuous white tubercles or dots on the anterior third of the carapace in hatchlings. Many adult males of _pallidus_ from the Brazos and some from the Trinity River drainages often have dusky or black ocelli surrounding the white dots posteriorly on the carapace; males from these river systems may be distinguished from _guadalupensis_ in having most, if not all, white dots on the anterior half of the carapace smaller than those posteriorly, and a pale brown carapace (in life, usually darker in _guadalupensis_). _T. s. pallidus_ (and _guadalupensis_) is distinguished from _emoryi_ in lacking a widened pale rim posteriorly, and in having small white spots on the anterior half of the carapace. _T. s. pallidus_ resembles _guadalupensis_ and _emoryi_ in having white spots on the carapace in adult males. _T. s. pallidus_ differs from _spinifer_, _hartwegi_ and _asper_ in lacking blackish dots or ocelli that occur in the center of the carapace. _T. s. pallidus_ resembles _emoryi_ but differs from _guadalupensis_ in lacking black ocelli surrounding the white spots. _T. s. pallidus_ resembles _spinifer_, _hartwegi_ and _asper_ but differs from _guadalupensis_ and _emoryi_ in having tubercles along the anterior edge of the carapace that are conical having sharp tips in males, and conical in large females.

_T. s. pallidus_ resembles _spinifer_ and _hartwegi_ but differs from the other subspecies in having a narrow head. _T. s. pallidus_ differs from _emoryi_ but resembles the other subspecies in having a wider carapace. _T. s. pallidus_ resembles _emoryi_ and _guadalupensis_, and differs from the other subspecies in having the carapace widest farther posterior than one-half the length of the carapace. The snout of _pallidus_ and _guadalupensis_ is shorter than in _spinifer_ and _hartwegi_, but longer than in _emoryi_. _T. s. pallidus_ differs from _asper_ but resembles the other subspecies in having a relatively long plastron.

_Remarks._--Intergradation of the subspecies _pallidus_ and _guadalupensis_ is of a clinal nature in which populations successively show a gradual resemblance to _guadalupensis_ from western Louisiana and eastern Texas westward to central Texas. Because the sharpest break in this cline of characters occurs between the Colorado and Brazos River drainages, the turtles living in the Brazos River drainage and eastward are referred to _pallidus_, whereas those in the Colorado River drainage and westward are referred to _guadalupensis_. For further comments on intergradation between these two subspecies, see the account of _T. s. guadalupensis_.

Taylor (1935:217-18) reported on some specimens of _Amyda spinifera_ that were obtained by Mr. R. E. McEntyre in "... the spring and summer of 1926, chiefly about Lewisville, Lafayette County (Arkansas)." Of the catalog numbers listed by Taylor from Lewisville, 58 (KU, alcoholic) represent _pallidus_. Three, having the same locality data, have features that are characteristic of _hartwegi_. KU 2944 (one of three specimens having this catalog number) is a female having a pale, mottled and blotched carapace approximately one foot in length; there are remnants of two dark ocelli, and many widely-scattered, well-defined dark spots near the periphery of the carapace. KU 2963 (one of three specimens having this catalog number) is an adult male that has solid, blackish dots on the entire surface of the carapace. KU 2964 (one of two specimens with this catalog number) is an adult male that has ocelli approximately five millimeters in diameter on the carapace (indistinct in center of carapace).

Lewisville is situated in the drainage basin of the Red River and is approximately eight miles east of the Red River and 30 miles west of the westernmost tributary of the Ouachita River drainage. _T. s. pallidus_ occurs in the Red River drainage; _hartwegi_ occurs in the Ouachita River drainage. Perhaps there is intergradation between _pallidus_ and _hartwegi_ in the intervening streams. There is no data to indicate from which river or stream each specimen obtained by McEntyre came; one would presume that all specimens came from the Red River drainage. But this is not certain. Certainly the 47 specimens designated herein as _pallidus_ came from the Red River drainage. I suspect that KU 2944, 2963 and 2964 were obtained from tributaries of the Ouachita River drainage.

_T. s. pallidus_ intergrades with the _spinifer-hartwegi_ population where the Red River joins the Mississippi River in the lower Mississippi Valley in Louisiana. The majority of 13 juvenal specimens from the Red River near Shaw, Concordia Parish, Louisiana (USNM 99862-69, 99871-75), resemble _pallidus_ in having inconspicuous white tubercles on a pale brown carapace. The white tubercles are conspicuous in USNM 99871. Some specimens have a few small dark dots confined to the margin of the carapace, as do some "variant" individuals from well within the geographic range of _pallidus_. USNM 99865 is referred to _hartwegi_ because the carapace is covered with dark ocelli approximately one millimeter in diameter. Some specimens from farther west in the Red River drainage are referred to _hartwegi_. One (USNM 100420) of three from Natchitoches Parish, Louisiana (TU 5763, USNM 100420-21), having blackish dots on the carapace, is applicable to _hartwegi_. Of two turtles from Grant Parish, Louisiana (TU 5647, 12735), only 12735 has dark dots and ocelli (_hartwegi_). One specimen from Rapides Parish, Louisiana (TU 14040), having dark dots on the entire surface of the carapace, is referred to _hartwegi_.

Most specimens from the lower Atchafalaya River drainage are referable to _pallidus_. Eastward, intergradation occurs with the _spinifer-hartwegi_ population; USNM 100089-90 from Assumption Parish, near Napoleonville, Louisiana, are referred to _pallidus_. TU 11983, from Bayou Lafourche, Raceland, La Fourche Parish, and TU 13698.11, from Bayou Gauche in St. Charles Parish, Louisiana, are juvenal males that combine the characteristics of _pallidus_ and _hartwegi_; the carapaces are covered with blackish spots and posteriorly have distinct whitish dots. The population in the Atchafalaya River more closely resembles _pallidus_ than it does _hartwegi_ or _spinifer_. In former times the Atchafalaya River was presumably continuous solely with the Red River (inhabited by _pallidus_). Now, these two rivers and the Mississippi River are interconnected in east-central Louisiana. A large volume of water of the Mississippi drainage is conveyed to the Gulf of Mexico by the Atchafalaya, and someone has said that by approximately 1975, unless man interferes, two-thirds to three-fourths of the total volume of water of the Mississippi River will be drained by the Atchafalaya. One can expect, therefore, an increase in the influence of the _hartwegi-spinifer_ population in the Atchafalaya River drainage.

_Specimens examined._--Total 270, as follows: ARKANSAS: _Lafayette_: KU 2930-37, 2939-40, 2942, 2944 (two of three specimens bear this catalog number), 2945-57, 2958 (2), 2959-61, 2963 (two of three specimens bear this catalog number), 2964 (one of two specimens bears this catalog number), 2965-73, 2987-89, 3056, Lewisville.

LOUISIANA: _Acadia_: USNM 100151-59, Mermentau River. _Assumption_: USNM 100089-90, Bayou Lafourche, "near" Napoleonville. _Beauregard_: TU 1231-32, 1253-55, 1291, 13211, 13266, Sabine River, 8 mi. SW Merryville. _Bienville_: TU 5649-50, Lake Bistineau. _Caddo_: TU 381, 397-99, 469-72, 474-90, 678, 10170, Caddo Lake: TU 15818-19, Cross Lake. _Calcasieu_: UMMZ 92754, 5 mi. W Iowa. _Cameron_: TU 1122, Lacassine Wildlife Refuge. _Concordia_: USNM 99862-64, 99866-69, 99871-75, Red River, "near" Shaw. _De Soto_: SM 2374-75, Wallace Bayou. _Grant_: TU 5647, Lake Iatt. _Iberville_: USNM 83985, 2 mi. E Mounds; USNM 100239-41, Grand Lake west of White Castle; USNM 100380, Plaquemine; USNM 100412, 100414-15, 100419, Spanish Lake, "near" St. Gabriel. _Jefferson Davis_: Calcasieu River drainage, WTN (no number, see page 524). _Natchitoches_: TU 5763, Bermuda; USNM 100421, "near" Natchitoches. _Sabine_: TU 13210, 13212-13, 13265, 13280-82, 13303-06, Sabine River, 8 mi. SW Negreet. _St. Martin_: USNM 100160, Bayou Chene; USNM 100650, Atchafalaya. _St. Mary_: USNM 100395-97, 100404, 100409-10, Berwick Bay near Morgan City.

OKLAHOMA: _Atoka_: OU 8966, Rock Creek, 10 mi. E Atoka; OU 8978, McGee Creek, 7 mi. SW Daisy. _Caddo_: ANSP 100, Washita River, Fort Cobb. _Choctaw_: OU 27126, Mayhew Creek, 2 mi. NW Boswell. _Comanche_: OU 4130, 4266, 5390, 8333, 12953, 19986, Wichita Mountains Wildlife Refuge. _Jackson_: OU 13012, 6 mi. E El Dorado. _Kiowa_: CNHM 15474. _Le Flore_: OU 6791, Kiamichi River, 8 mi. W Arkansas State Line. _McCurtain_: OU 2149-50, 2152, 2155, 17126-28, 17185, 2 mi. SW Smithville; USNM 70397, Red River. _Marshall_: KU 40175-76, 50830-31, 50847, OU 27290, 27297, 27562-63, TU 16076 (5), 16175 (6), 16662 (5), Lake Texoma, 2 mi. E Willis; KU 50832, mouth of Caney Creek, 4 mi. SW Kingston. _Pushmataha_: OU 2151, 2157; OU 11365, Buffalo Creek, 5 mi. NW Tuskahoma.

TEXAS: _Archer_: TU 16174, 16668-69, Lake Diversion. _Bell_: SM 5667-69, Nolan Creek. _Bosque_: KU 47121, 7 mi. below Whitney Dam, Brazos River. _Brazos_: BCB 4436, 10 mi. E College Station; BCB 4437, 17 mi. S College Station; BCB 4438, 4 mi. N Bryan; KU 50833, 4 mi. W College Station; SM 2556, TCWC 472, Wickson Lake; TCWC 539, Little Brazos River; TCWC 4692, 8 mi. NE Bryan; TCWC 5121, 2 mi. S College Station; TCWC no number. _Clay_: TCWC 7258, 8 mi. NW Ringgold, Montague County; TU 16667.1, 3 mi. W Byers. _Dallas_: MCZ 3987, "near" Dallas; ANSP 13243, Dallas. _Donley_: ANSP 13440, S of Clarendon. _Eastland_: KU 3132, Cisco. _Galveston_: TCWC 7251, Alta Loma. _Harris_: UMMZ 92753, Little Cypress Creek, 1 mi. N Westfield; USNM 94335-36, "near" Houston. _Harrison_: USNM 95386, 16.5 mi. SE Caddo Lake. _Hill_: TU 14169, Richland Creek, 0.7 mi. W Mertens. _Leon_: CNHM 46290, 5 mi. W Marquez; TCWC 8994, 8996, 6 mi. NW Normangee. _Liberty_: TU 14402, 14417, Trinity River, "near" jct. with Big Creek. _McLennan_: BCB 4665-66, 6 mi. NNE McGregor; SM no number, 2037, 2452, 2552, 2558, 2560, 2640, 5263, 6533, Lake Waco; SM 0185, Middle Bosque River; SM 2104, 6732, Upper Bosque River; SM 5072, Bull Hide Creek; UI 2399, 1.5 mi. W China Springs; UMMZ 64063, Waco; USNM 55601. _Madison_: TCWC 471, 517, Twin Lakes. _Montgomery_: TCWC 540, 3 mi. S Conroe. _Nacogdoches_: TNHC 14112, Legg Creek, 5 mi. S Douglass. _Orange_: UMMZ 117060, 3 mi. S Orange; USNM 94456-57, Orange. _Randall_: TTC 576, Palo Duro Canyon, 15 mi. SE Canyon. _Shackelford_: TU 14547, Clear Fork Brazos River, Fort Griffin State Park. _Somervell_: TCWC 8995, TU 14559 (4), Brazos River, 5-6 mi. E Glen Rose. _Trinity_: SM 2889, Groveton. _Walker_: TNHC 20829, 5 mi. E New Waverly. _Waller_: TNHC 14068, 2.7 mi. E Brazos River on US 90. _Williamson_: MCZ 1627 (2); TU 14348, San Gabriel River, 6.5 mi. E Georgetown. _County unknown_: ANSP 13448, Wichita River; USNM 7640, Brazos River.

_Records in the literature._--LOUISIANA: _Cameron_: Sabine Refuge (Cagle and Chaney, 1950:386).

OKLAHOMA: _Le Flore_: 6 mi. W Page. _McCurtain_: 14 mi. SE Broken Bow (Trowbridge, 1937:301).

TEXAS: _Bosque_: Bosque River, "near" Valley Mills (Strecker, 1928:6). _Harris_: Addicks (Brown, 1950:250). _Henderson_: Cedar Creek (Strecker, 1926a:7). _Jefferson_: 12 mi. SW Port Arthur (Guidry, 1953:56). _Liberty_: Daisetta (Brown, _loc. cit._); San Jacinto River (Strecker, 1915:15). _McLennan_: "near" Crawford (Brown, _loc. cit._). _Orange_: 1 mi. N Bridge City (Guidry, _loc. cit._). _Tarrant_: Trinity River, Fort Worth (Stejneger, 1944:66). _Taylor_: Abilene (KKA). _Tyler_: Colmisneil (Siebenrock, 1909:603). _Walker_: 6 mi. E Huntsville (TCWC 329, listed in card file). _Wheeler_: 5 mi. N Wheeler (Brown, _loc cit._).

=Trionyx ater= Webb and Legler

Black Softshell

_Trionyx ater_ Webb and Legler, Univ. Kansas Sci. Bull., 40:21, pls. 1 and 2, 1960, April 20.

_Type._--Holotype, KU 46903, alcoholic female; obtained 16 km. S Cuatro Ciénegas, Coahuila, México, by John M. Legler (and party), September 6, 1958.

_Range._--Basin of Cuatro Ciénegas, central Coahuila, Mexico (see map, Fig. 22).

_Diagnosis._--Posterior margin of carapace of some females having fine corrugations, edge often ragged, and no pale outer margin; septal ridges reduced in adult males; over-all dorsal coloration (in preservative) dark, lacking contrasting patterns.

_Description._--Plastral length of adult male, 9.6 centimeters (KU 46911); of largest female, 18.4 centimeters (KU 46903).

Adult male: anterior edge of carapace smooth; septal ridges reduced; pale outer rim, and small, whitish, dots posteriorly on carapace; surface of carapace slightly gritty or sandpapery posteriorly; snout broadened; over-all dorsal coloration dark gray or slate; contrasting pattern on soft parts of body lacking; ventral surface whitish having few blackish marks posteriorly on undersurface of carapace.

Females: posterior margin of carapace usually having fine corrugations; edge of carapace posteriorly often ragged; pale rim of carapace absent; mottled and blotched pattern not contrasting on blackish carapace; dorsal surface of soft parts of body dark gray or slate, lacking contrasting pattern; ventral surface of carapace and posterior part of plastron usually having many blackish flecks and markings; tubercles lacking on anterior edge and in center of carapace posteriorly; septal ridges well developed.

Medial angle of epiplastron (as observed through overlying skin) bent at angle of approximately 90 degrees. Other osteological characters presumably as in _spinifer_.

Range in length of plastron (cm.) of 11 females (mean follows extremes); 10.8-18.4, 15.0; proportional measurements of 12 specimens (including adult male, mean follows extremes): PL/HW, 4.70-5.43, 4.93; CL/CW, 1.28-1.43, 1.32; CL/PCW, 1.98-2.42, 2.15; HW/SL, 1.22-1.58, 1.37; CL/PL, 1.29-1.44, 1.36; some females (especially KU 46908) have noticeably elongate carapaces.

_Variation._--Corrugations best developed on two largest females (KU 46903, 46906), even present on ventral surface of carapace posteriorly and on dorsal surface of tail; development of corrugations not ontogenetic phenomenon as posterior margin relatively smooth on KU 46908 (plastral length, 16.0 cm.) but relatively rugose on KU 46909, which is smaller (plastral length, 13.9 cm.); smallest female (KU 46904) and adult male having posterior margin smooth; smallest female having indication of pale outer rim and small whitish dots posteriorly on carapace, and dark, obtusely-angular line, connecting anterior margins of orbits; blackish marks on ventral surface reduced on KU 46904, 46910, 46912, and UI 43510; UI 43510 (plastral length, 16.3 cm.) resembles _T. s. emoryi_ in having more contrasting mottled pattern on carapace and limbs, indication of pale outer rim on carapace, and dark line connecting anterior margins of orbits; ventral surface of tail and hind limbs often tinged with red.

Color notes from life of young female, topotype (KU 53755) are: mottled carapace dark brown, pale areas buff; dorsal surface of head mottled, olive-brown, pale areas buff; iris orange-buff; upper and lower lips yellow-orange; dorsal surface of limbs olive-brown having yellow to buff suffusion and small blackish marks; pale areas on webbing yellow; ventral surface whitish having yellow at margin of carapace, on neck and limbs.

_Comparisons._--_T. ater_ most closely resembles _T. spinifer_ (especially the subspecies _emoryi_) in having a gritty or "sandpapery" carapace (reduced, tubercles more scattered), whitish dots on posterior third of carapace (small females and adult male) and a dark line connecting anterior margins of orbits (smallest female). Prior to acquiring the characteristic darkened, dorsal ground color, the pattern on the head and limbs seems to be that of _T. s. emoryi_.

_T. ater_ resembles _T. muticus_ in having reduced septal ridges in males, a smooth anterior edge of carapace (especially males), and no enlarged prominences on the anterior edge of the carapace or posteriorly in the center of the carapace on large females. _T. ater_ resembles _T. ferox_ in having an over-all dark coloration dorsally with no contrasting patterns on adults.

_T. ater_ probably is a small species resembling _T. muticus_ and _T. spinifer emoryi_. The head is wide in _T. ater_, resembling that of _T. ferox_, and closely approaching that of _T. spinifer emoryi_ and _T. s. guadalupensis_. _T. ater_ resembles _T. ferox_ and _T. s. emoryi_ in having a narrow carapace. _T. ater_ resembles _T. s. emoryi_, _T. s. guadalupensis_ and _T. s. pallidus_, but differs from _T. muticus_, _T. ferox_ and the other subspecies of _T. spinifer_ in having the carapace widest farther posterior than one-half the length of the carapace. _T. ater_ resembles _T. ferox_ and _T. s. emoryi_ in shortness of snout. The plastron is short in _T. ater_ and most closely resembles that of _T. s. pallidus_, _T. s. guadalupensis_, and _T. s. emoryi_.

_Remarks._--_T. ater_ is confined to permanent, clear-water ponds in the basin of Cuatro Ciénegas. The male and 11 females (KU) were taken at the type locality (a pond known locally as Tío Candido); the other female (UI 43510) was taken from a pond approximately seven miles northward (known locally as Anteojo). _T. spinifer emoryi_ also occurs in the basin of Cuatro Ciénegas. Males and females of _emoryi_ were collected in the Río Mesquites (Río Salado drainage) that drains the basin; two adult males of _emoryi_ were taken from the clear-water ponds--one from the type locality of _ater_ (KU 46907), and the other (KU 53757) from a pond (known locally as El Mojarral) from which no _ater_ were obtained. This demonstrated sympatry indicates that the two kinds are not conspecific.

However, the nature and frequency of occurrence of characters of _T. ater_, suggest that it is subspecifically related to _T. spinifer_--in effect, a darkened race of _T. s. emoryi_. The diagnostic characters of fine corrugations on the posterior margin of the carapace and blackish marks on the ventral surface do not occur on every female of _ater_. Too, the dorsal coloration of living females (dark brown-buff) is paler than that of preserved specimens (dark gray-slate). Furthermore, a hatchling (CNHM 47367) recorded from Cuatro Ciénegas, Anteojo, is not distinguishable from _emoryi_.

The mention of absence of septal ridges in males of _T. ater_ in the original description (Webb and Legler, 1960:22) should be amended. The septal ridges in the only known adult male are reduced; a small, whitish ridge is present on the medial surface of each nostril, but is not conspicuous in anterior view. The one adult male of _ater_ is distinguished from _T. s. emoryi_ principally on the over-all dark, dorsal coloration with concomitant loss of pattern, the noticeably broadened snout, and the reduced septal ridges. The last character mentioned possibly is variable in _ater_ (and in _emoryi_ in this region) in view of the variation in development of the ridge on four male _emoryi_ from the basin: well-developed on KU 53757 (Mojarral) and KU 46907 (Tío Candido); reduced on KU 53752 (Río Mesquites), resembling development in _ater_; and, reduced on right side only on KU 53753 (Río Mesquites).

Presumably, the continued erosive action at the headwaters of the Río Salado has permitted the invasion of this drainage into the formerly isolated basin of Cuatro Ciénegas. In the basin, however, I know of no evidence of a direct aquatic contact between the headwater streams and the isolated, clear-water, ponds. How _emoryi_ entered the ponds is unknown. Some of the ponds are tapped by small, man-made, irrigation canals, but, so far as I know, these are not connected to the river. The ponds have permanent water and are often separated by several miles of arid environment. Overland dispersal between waterways is possible in time of flooding. Local residents tell of the infrequent sale of softshells in Cuatro Ciénegas, which hints at their dispersal via the agency of man. The underlying gypsum substrate of the valley has been subjected to considerable erosion; the ponds observed have deep holes, and small caverns and grottos. There are conflicting reports concerning subterranean connections between ponds. Possibly there are underwater connections between some ponds and the headwater streams of the Río Mesquites. Whatever the dispersal route for _emoryi_ into the ponds has been, it is strange that the same route has not been traversed by _ater_, permitting its occurrence in the Río Mesquites.

On the basis of morphological criteria, I suspect that _ater_ and _emoryi_ are genetically compatible. Possibly there is only sporadic entrance of _emoryi_ into the ponds inhabited by _ater_, or the accessible dispersal routes for _emoryi_ have been relatively recent and there has been insufficient time for genetic adaptation. _T. ater_ is maintained as a full species because of the occurrence of two distinct males (KU 46907, _emoryi_, and KU 46911, _ater_) in the same pond (Tío Candido, the type locality). These two specimens are contrasted in a photograph accompanying the type description (Webb and Legler, 1960: Pl. II). The restricted distribution of _ater_, and its characteristics suggest a relict population derived from a _ferox_-like ancestor that may be in the process of becoming extinct.

There are two specimens in the CNHM recorded from Cuatro Ciénegas. One is a female (CNHM 55661) having a plastral length of 19.0 centimeters, and no specific locality other than Cuatro Ciénegas. I examined this specimen before I knew of the existence of _ater_, and noted no unusual features; I have not re-examined the specimen. It is considered representative of _emoryi_. The second is a hatchling (CNHM 47367) having a plastral length of 3.2 centimeters, recorded from Cuatro Ciénegas, Anteojo. The carapace is dark tan having small whitish dots intermixed with a few indistinct, small, blackish specks posteriorly. The specimen is indistinguishable from _emoryi_.

_Specimens examined._--Total 12, as follows: COAHUILA: KU 46903-06, 46908-12, 53755-56, 16 km. S Cuatro Ciénegas; UI 73510, 5.7 mi. W Cuatro Ciénegas.

_Records in the literature._--Schmidt and Owens (1944:103) record _emoryi_ from Cuatro Ciénegas (no museum numbers listed); presumably their reference is to CNHM 55661.

=Trionyx muticus= Lesueur

Smooth Softshell

_Range._--United States from extreme western Pennsylvania, southern Minnesota and South Dakota south to the Gulf of Mexico in Alabama, the western end of the panhandle of Florida, and the eastern half of Texas (see map, Fig. 22.)

_Diagnosis._--Septal ridges absent; anterior edge of carapace smooth, lacking prominences; juvenal pattern of large dusky spots (sometimes ocellate), or small dusky (not black), dots and short lines; side of head usually devoid of markings except for pale, usually uninterrupted, postocular stripe.

Size small; head narrow; snout long; ventral surface of supraoccipital spine broad proximally, lacking median ridge; foramen magnum evenly rounded, ovoid; opisthotic-exoccipital spur absent; distal part of opisthotic wing truncate; lateral condyle of articular surface of quadrate tapered posteriorly, smaller than medial articular surface; angle of epiplastron obtuse, approximately 100 degrees; callosity on epiplastron sometimes covering entire surface; bony bridge wide in relation to length.

_Description._--Septal ridges absent; external characteristics variable (see accounts of subspecies); range in length, in centimeters, of plastron of ten largest specimens of each sex, (mean follows extremes), males, 11.8-14.0, 12.3; females, 17.7-21.5, 18.9; ontogenetic variation in PL/HW, mean PL/HW of specimens having plastral lengths 7.0 centimeters or less, 4.16, ranging from 7.1 to 13.0 centimeters, 5.82, and, exceeding 13.0 centimeters, 7.04; little ontogenetic variation in CL/CW, mean CL/CW of specimens having plastral lengths 8.0 centimeters or less, 1.15, and exceeding 8.0 centimeters, 1.16; mean CL/PCW, 1.97; mean HW/SL, 1.22; mean CL/PL, 1.39.

Greatest width of skull usually at level of squamosal (79%); foramen magnum ovoid; opisthotic-exoccipital spur usually absent (97%); distal part of opisthotic wing truncate, sometimes visible in dorsal view; lateral condyle of articular surface of quadrate tapered posteriorly, smaller than medial articular surface; maxillaries not in contact above premaxillaries; combination of seven neurals, seven pairs of pleurals, and contact of seventh pair of pleurals (38%), or eight neurals, seven pairs of pleurals, and separation of seventh pair of pleurals (41%); angle of epiplastron obtuse, greater than 90 degrees; callosities well-developed, frequently on preplastra and epiplastron of adults.

_Comparisons._--The absence of septal ridges distinguishes _muticus_ from _ferox_, all subspecies of _spinifer_, and _ater_ (ridges are reduced in males of _ater_). The smooth anterior edge of the carapace distinguishes _muticus_ from all other American kinds except _ater_ and some individuals of _T. s. emoryi_. _T. muticus_ resembles only _ater_ and _ferox_ in usually lacking a well-defined, contrasting pattern of blackish marks on the dorsal surface of the limbs. _T. muticus_ resembles _ferox_ and differs from _spinifer_ and _ater_ in lacking a gritty or "sandpapery" carapace on adult males. Adult males of _T. muticus calvatus_ and some individuals of _T. m. muticus_ from the Colorado River in Texas further resemble _ferox_ in having postocular stripes with thick black borders.

_T. muticus_ is the smallest species in North America; the maximum size of the plastron in adult males is approximately 14.0 centimeters (16.0 cm. in _spinifer_) and of adult females 21.5 centimeters (31.0 cm. in _spinifer_). Males and females of _muticus_ are sexually mature at approximately the same size as some _T. s. emoryi_; also, the great development of the plastral callosities in _muticus_ corresponds to that in some _emoryi_. The head is narrower in _muticus_ than in _ferox_ or _spinifer_. The carapaces of specimens of _muticus_ exceeding plastral lengths of 8.0 centimeters are wider than those of _ferox_, _ater_, _T. s. emoryi_ and _T. s. guadalupensis_ of corresponding size. _T. muticus_ differs from _ater_ and three subspecies of _spinifer_ (_pallidus_, _guadalupensis_, _emoryi_) in having the carapace widest at a plane approximately one-half the length of the carapace. The snout is longer in _muticus_ than in _ferox_ and _spinifer_. _T. muticus_ differs from _ferox_ but resembles _spinifer_ in having a relatively short plastron.

The skulls of _muticus_ differ from those of _ferox_ but resemble those of _spinifer_ in usually having the skull widest at the level of the squamosals. Skulls of _muticus_ resemble those of _ferox_ but differ from those of _spinifer_ in usually lacking a well-developed opisthotic-exoccipital spur. Skulls of _muticus_ are different from those of _ferox_ and _spinifer_ in having the 1) ventral surface of the supraoccipital spine widest proximally, lacking a medial ridge, 2) foramen magnum ovoid, 3) distal part of opisthotic wing truncate, 4) lateral condyle of articular surface of quadrate tapered posteriorly, smaller than medial articular surface, and 5) maxillaries not in contact above premaxillaries.

Plastrons of _muticus_ differ from those of _spinifer_ and _ferox_ in having an obtusely-angled epiplastron, relatively large callosities in adults, and a wide hyo-hypoplastral bridge (in relation to length).

_Remarks._--Agassiz (1857:399) regarded Lesueur's _Trionyx muticus_ as the type species of the genus _Amyda_ and the only species known to belong to the genus _Amyda_. Stejneger (1944:7, 9, 12) proposed the generic name _Euamyda_ as a new name for the North American _Amyda mutica_ as understood by Agassiz. _Euamyda_ was proposed for use only if Agassiz's understanding was found to be correct. Actually, Stejneger thought that the Old World and New World kinds concerned were congeneric, and that the type species of the genus _Amyda_ was the Old World species _Amyda javanica_ Schweigger (= _Testudo cartilaginea_ Boddaert).

If _Trionyx muticus_ Lesueur is considered to be generically distinct from other soft-shelled turtles, _Euamyda_ Stejneger, 1944, is available as a generic name with _Trionyx muticus_ Lesueur, 1827, as the type species (by monotypy).

_Geographical variation._--_Trionyx muticus_ shows no obvious character gradients; the variation is mostly discontinuous and unlike that in _T. spinifer_. On the basis of differences in the juvenal pattern and pattern on head, _T. muticus_ can be divided into two subspecies.

=Trionyx muticus muticus= Lesueur

Midland Smooth Softshell

Plates 45, 46, and 53

_Trionyx muticus_ Lesueur, Mém. Mus. Hist. Nat. Paris, 15:263, pl.7, December, 1827.

_Trionyx muticus muticus_ Webb, Publ. Mus. Nat. Hist. Univ. Kansas, 11:520, August 14, 1959.

_Potamochelys? microcephala_ Gray, Proc. Zool. Soc. London, p. 87, 1864.

_Type._--Lectotype, Museum d'Histoire Naturelle, Paris, No. 8813; dried carapace and plastron; obtained from the Wabash River, New Harmony, Posey County, Indiana, by C. A. Lesueur in August, 1827 (Pl. 53).

_Range._--Central United States; in the Mississippi River drainage from extreme western Pennsylvania, southern Minnesota and South Dakota south to Tennessee, Louisiana and Oklahoma; streams of the Gulf Coast drainage from the Mississippi River in Louisiana westward into Texas including the Colorado River drainage (see map, Fig. 22).

_Diagnosis._--Juvenal pattern of dusky dots and usually short lines or bacilliform marks; ill-defined pale stripes on snout usually evident just in front of eyes; pale postocular stripe lacking thick, black borders that are approximately one-half width of pale stripe (except some in the Colorado River drainage of Texas).

_Description._--Plastral length of smallest hatchling, 2.1 centimeters (INHS 3458); of largest male, 14.0 centimeters (CNHM 92003); of largest female, 21.5 centimeters (KU 2308).

Juvenal pattern of dusky, grayish marks lacking sharp margins, and usually consisting of both small spots and short streaks or dashes, the former predominating; short streaks or dashes occasionally lacking (TU 14375, Pl. 45, bottom, left; UMMZ 92751); markings variable in number, few and widely spaced, or several and closely approximated (Pl. 45, top, topotypes); pale rim separated from ground color by ill-defined, dusky margin; pattern on adult males well-defined resembling that of hatchlings (TU 16172.1, 16173), scarcely discernable (TU 13294), or absent (TU 1242); mottled and blotched pattern on carapace usually contrasting in large females.

Pale stripes extending forward from eyes usually not more than half distance to tip of snout; inner borders of pale stripes on snout usually absent or dusky and indistinct, occasionally blackish (TU 14606); outer borders of pale stripes darker than inner borders, usually blackish; pale stripes on snout occasionally absent (CNHM 7845, UMMZ 92665, TU 5989, none of these specimens being large females); pale postocular stripe having narrow, dusky or blackish borders (especially UMMZ 92751, TU 14436); pale postocular stripe usually complete, occasionally interrupted having prominent dark-bordered anterior segment just behind eye (TU 14416); lower border of postocular stripe usually in contact with dusky postlabial line; no other markings on side of head; pattern on dorsal surface of soft parts of body not contrasting, composed of closely approximated fine markings that are little darker than background, over-all coloration pale grayish; occasionally, few larger and more contrasting markings on hind limbs (UMMZ 92751, TU 14436).

Underparts white, usually lacking markings; occasional dusky markings on plastral area (UMMZ 110502), dark spots or flecks on undersurface of carapace (BCB 6043, UMMZ 92666), or markings on throat (UMMZ 95032).

Surface of carapace smooth in adult males; large females lacking prominences posteriorly in center of carapace or in nuchal region; anterior edge of carapace smooth in both sexes, but occasionally having regularly spaced furrows or wrinkles (Fig. 8g).

_Variation._--Short dusky lines and streaks seem to be lacking from the juvenal pattern on the carapace more often in southern populations (Gulf Coast drainage of Texas) than in northern populations (Mississippi River drainage). I have seen one female, KU 48229 (Pl. 46, bottom, left), plastral length 14.5 centimeters that retained a well-defined juvenal pattern, and lacked a mottled and blotched pattern.

Color notes from life of 11 turtles, KU 55296-306, (eight adult males, three immature females) from the Kansas River at Lawrence, Douglas County, Kansas, are: Buff-yellow rim of carapace, sometimes having pale orange tinge; dusky, dark brown markings on pale brown or tannish carapace of males; dark and pale brown mottled and blotched pattern on carapace of females (smallest specimens having plastral length, 11.0 cm.), many having orangish or buffy hue; soft parts of body brownish to olive-green dorsally, many having small, blackish marks on hind limbs; webbing of limbs yellowish; pale orange, some yellow, laterally at juncture of dark dorsum and pale ventrum (to a lesser extent on hind limbs); pale orange in some suffusing onto dorsal surface of soft parts of body; black-bordered postocular stripes in males having orangish tinge (pattern somewhat obscured in females); whitish ventral surface in some having pale orangish tinge here and there; many having dusky, grayish flecking on plastral area and anterior ventral surface (most intense on 55306 giving appearance of grayish suffusion).

I have seen only three specimens from the Colorado River drainage in Texas. Two of these (UMMZ 92751, TU 14436) are characterized by much black pigmentation. A contrasting pattern of relatively large black marks occurs on the dorsal surface of the soft parts of the body, especially on the hind limbs, and the pale postocular stripes have thick black borders. UMMZ 92751, having a plastral length of 5.5 centimeters, has a juvenal pattern of widely-spaced dark dots that lacks short lines. The other _muticus_ from the Colorado River (CM 3055), a large female 19.0 centimeters in plastral length, has ill-defined postocular stripes lacking dark borders, although a small dusky blotch occurs on the right side of the head.

_Comparisons._--_T. m. muticus_ differs from _T. m. calvatus_ in having pale stripes on the snout, a juvenal pattern of small dusky spots (usually lacking ocellate spots) and short lines, and a pale postocular stripe lacking thick, blackish borders (except in some turtles from the Colorado River system of Texas). One unique characteristic of _muticus_ is the short, dusky lines in the juvenal pattern; these marks, however, are occasionally absent.

_Remarks._--_Trionyx muticus_ generally has been considered a distinct species since its description by Lesueur (1827:263-66, Pl. 7); Wied-Neuwied (1865:53), at least, questioned the identity of _muticus_, believing it to be based on a secondary sexual difference of _T. spiniferus_. Lesueur did not designate a type in the description, and mentioned that he had seen only three specimens (_op. cit._:264). Stejneger (1944:17-18) discussed two mounted specimens (Nos. 787 and 788) in the Natural History Museum at Paris, and mentioned that No. 787 was designated "... as the type on the printed label (although presumably not done by Lesueur)." Dr. Jean Guibé (_in litt._ September 24, 1959) informed me that Nos. 787 and 788 are numbers without value and correspond, respectively, to catalog numbers 8813 and 8814. In addition, the Museum possesses an alcoholic specimen, No. 564, obtained by Lesueur from the Wabash River, that seems to have been acquired by the museum after the publication of the original description. No. 8813 is regarded as a lectotype.

Gray (1864:87) described the species _microcephalus_ and questionably included it in the genus _Potamochelys_ Fitzinger, 1843; the locality was stated as "Sarawak (Wallace)." Gray especially noted the small elongate head and believed that the acquisition of adult specimens would prove that it belonged to a new genus. Later, Gray (1869:221) proposed the generic name _Callinia_ as a new name for _Aspidonectes_ as understood by Agassiz (1857:403). Gray referred _microcephala_ to _Callinia_ (_op. cit._:214, 222) and recognized also _Amyda mutica_ (_op. cit._:212). Baur (1888:1121) remarked that "_Callinia microcephala_ Gray, of the British Museum, with the locality Sarawak, is _Amyda mutica_ Les." The species _microcephalus_ has since been considered a synonym of _Trionyx muticus_. Schmidt (1953:110) designated the type locality as New Harmony, Indiana.

Müller (1878:641) listed the species _Trionyx muticus_ from México as follows: "*b. in Alcohol. Mexico. 1872. [2]." Smith and Taylor (1950:18, footnote) wrote that the record required confirmation. Webb and Legler (1960:24) questionably referred this record to the synonomy of _T. ater_, which resembles _muticus_. _T. muticus_ is not known to occur in México. According to Dr. Lothar Forcart (_in litt._) of the Naturhistorische Museum in Basel, Switzerland, only one specimen on which Müller based his record is extant. My examination of this specimen reveals that it is a hatchling _T. s. emoryi_, plastral length 3.5 centimeters, bearing catalog number 1032; there are no additional data of collection.

Strecker and Williams (1927:16) mentioned one specimen of _muticus_ that was obtained at Christoval, Tom Green County, Texas, and I presume this is the basis for Pope's mention of this species from Tom Green County, Texas (1949:319). Although I do not doubt that _T. muticus_ occurs in Tom Green County, this record possibly is based on _T. spinifer_ because, 1) there are no specimens of _muticus_ in the Strecker Museum from Tom Green County, but there is one specimen of _spinifer_ (SM 3282), and in none of Strecker's publications is there any mention of _spinifer_ from Tom Green County, and 2) Strecker had, at least once, misidentified the two species; his record of _muticus_ from Wallace Bayou, Louisiana (Strecker and Frierson, 1926:last page, no numbers), represents _T. spinifer pallidus_ (SM 2374-75).

_Specimens examined._--Total 261, as follows: ALABAMA: _County unknown_: USNM 118167, Wheeler Reservoir, Tennessee River.

ARKANSAS: _Franklin_: KU 19459-60, Ozark. _Lafayette_: KU 2938, 3057, Lewisville. _Lawrence_: CNHM 92003, Imboden; CNHM 92005, Powhatan; USNM 59214, Black River, Black Rock. _Marion_: TU 14606 (2), White River at Cotter. _Prairie_: KU 1831, 1868, 1870, 1874-76, 1930-31, 1957-63, 2294-302, 2305-06, 2308-09, 2838-41, 3002, White River, DeVall's Bluff.

KANSAS: _Barber_: USNM 95185-86, 1 mi. S Lake City. _Doniphan_: KU 1872, 1878, 1964, Doniphan Lake. _Douglas_: KU 2220, 16148, 23230, 40179, 50825-26, 55296-306, Kansas River, Lawrence; KU 45065-66, 1 mi. N, 1.5 mi. W Lakeview. _Ford_: KU 51516, Ford. _Kearny_: KU 48216, 4 mi. S, 1.5 mi. W Deerfield. _Marshall_: KU 48228, Blue Rapids. _Pottawatomie_: KU 48229-33, 48238, 2 mi. E Manhattan, Riley County. _Reno_: USNM 95260, 6 mi. E Turon. _Riley_: KU 46861, 48234-35, 4 mi. N Manhattan; KU 48236, 2 mi. NE Randolph. _Sedgwick_: UMMZ 95362, Wichita. _Shawnee_: UMMZ 95366-67, Topeka. _Sumner_: USNM 95415, 3 mi. SE Oxford. _Washington_: KU 48237, 8 mi. S Hanover. _Woodson_: KU 45064, 1 mi. E, 2 mi. S Neosho Falls. _County unknown_: USNM 51528.

ILLINOIS: _Cass_: INHS 2146, Beardstown. _Coles_: INHS 1965-67, 3 mi. S Charleston. _Jackson_: INHS 5894, 6.5 mi. N Aldridge, Union County; UMMZ 81570, Mississippi River. _Jasper_: INHS 2412, Rose Hill. _Jersey_: INHS 2156-58, Grafton. _Mason_: INHS 2147, Cedar Creek. _Mercer_: INHS 3458, Keithsburg. _Monroe_: INHS 4088, 3 mi. NE Columbia. _Morgan_: CNHM 6028, INHS 2148, Meredosia. _Pope_: CNHM 2463 (30), Golconda. _Schuyler_: UI 40-41, Crooked Creek. _Shelby_: INHS 2283, Holliday. _Wabash_: INHS 5228, Mt. Carmel.

INDIANA: _Daviess_: UMMZ 110234, White River, 1.5 mi. W Elnora. _Jefferson_: USNM 8337, Madison. _Knox_: UMMZ 111880-81, "near" Decker Chapel. _Posey_: INHS 7278-80, 7447, TTC 798, Wabash River, 2-2.5 mi. S New Harmony; UMMZ 110598, 8 mi. NW Mt. Vernon.

IOWA: _Allamakee_: UMMZ 92657, 1/4 mi. W Victory, Vernon County, Wisconsin; UMMZ 92658-64, Mississippi River, "near" Lansing. _Boon_: UMMZ 92665, Des Moines River at Ledge State Park. _Greene_: UMMZ 92666, 3.5 mi. N Scranton. _Muscatine_: USNM 53521, 54733-34, 54742, 60054-56, Fairport.

LOUISIANA: _Beauregard_: TU 1242, Sabine River, Merryville. _Caddo_: CNHM 7845, Gayles. _Catahoula_: USNM 113228, Jonesville. _Concordia_: USNM 99870, Red River, "near" Shaw. _Ouachita_: TU 5989, Monroe. _Richland_: USNM 100422, Rayville. _Sabine_: TU 13163, 13294, Sabine River, 8 miles SW Negreet. _St. James_: TU 7543, Vacherie. _St. Mar_: USNM 100406, Berwick Bay, "near" Morgan City. _Vernon_: KU 41380, 46777, Sabine River NW Burr Ferry.

MINNESOTA: _Hennepin_: AMNH 4761-62, Fort Snelling.

MISSISSIPPI: _Washington:_ USNM 92605, Greenville. _County unknown_: USNM 115939.

MISSOURI: _Clark_: USNM 59267, 59278, Alexandria. _Daviess_: UMMZ 95505, Grand River, 1 mi. S Jameson. _St. Louis_: SM 2052, St. Louis. _Wayne_: UMMZ 82823, St. Francis River.

NEBRASKA: _Webster_: UMMZ 89526, Republican River, 2 mi. E Inavale.

OKLAHOMA: _Cleveland_: OU 5480-81, 6473, South Canadian River, 4 mi. SE Norman. _Hughes_: KU 50845, 4 mi. N Atwood. _Kay_: OU 9741, 8 mi. E Ponca City. _Le Flore_: OU 2148; OU 27390, Poteau River below Wister Dam. _Love_: OU 27472, Hickory Creek, 9 mi. E Marietta. _Major_: OU 8597, 7 mi. E Orienta. _Marshall_: KU 50827-29, 50848, 50853, OU 27593-94, TU 16077 (4), Lake Texoma, 2 mi. E Willis. _McIntosh_: OU 8993, 4 mi. W Onapa. _Oklahoma_: OU 10137, Lake Oberholser. _Payne_: UMMZ 89629, Cimarron River, 3 mi. E Ripley; UMMZ 90002, 19 mi. SE Stillwater. _Pottawatomie_: OU 25176-83, South Canadian River, 5 mi. SW Shawnee. _Roger Mills_: OU 12472. _Sequoyah_: OU 9006, Illinois River, 2 mi. NE Gore. _Tulsa_: UMMZ 95032 (4), Arkansas River at Tulsa. _Woodward_: CNHM 15472-73; OU 8599-600, 5 mi. E, 1 mi. N Woodward.

SOUTH DAKOTA: _Yankton_: UMMZ 110499-500, Missouri River at Fort Randall; UMMZ 110501-02, Missouri River at Yankton.

TENNESSEE: _Benton_: UMMZ 53198, Trotter's Landing. _Lake_: USNM 102677, Reelfoot Lake. _Obion_: USNM 102910, Reelfoot Lake.

TEXAS: _Archer_: TU 16173, Lake Diversion. _Baylor_: TU 16172 (2), Lake Kemp. _Brazos_: TCWC 7250, Bryan. _Clay_: TCWC 7248-49, 7259-61, 8 mi. NW Ringgold, Montague County; TU 16667, 3 mi. W Byers. _Grayson_: UI 2419, Lake Texoma. _Gregg_: SM 6685, near Gladewater; USNM 22629, Sabine River, 5 mi. S Longview. _Liberty_: TU 14416, 14375, Trinity River, "near" jct. with Big Creek. _McLennan_: BCB 6030, 6043, SM 2557, 2561, Lake Waco. _Matagorda_: CM 3055, Colorado River, Bay City. _San Saba_: TU 14436, San Saba River, 11 mi. NNW San Saba. _Tarrant_: UMMZ 92750, Worth Lake, Fort Worth. _Wharton_: UMMZ 92751, Colorado River, Wharton.

NO DATA: MCZ 1594 (erroneously recorded from Mobile, Alabama); USNM 029261, 59982.

_Records in the literature._--ARKANSAS: _Garland_: Hot Springs (Combs and Hurter _in_ Strecker, 1924:47). _Jefferson_: Pine Bluff. _Pulaski_: Little Rock. _Sebastian_: Fort Smith (Hurter and Strecker, 1909:21).

ILLINOIS: _Adams_: Quincy (Garman _in_ Cahn, 1937:179). _Alexander_: Horseshoe Lake (Cahn, _loc. cit._); Cairo (Garman _in_ Cahn, _loc. cit._). _Carroll_: 5 mi. S Savanna (Stejneger, 1944:24). _Clay_: Louisville. _Clinton_: Carlyle. _Crawford_: Robinson (Cahn, _loc. cit._). _Cumberland_: Embarrass River (Peters, 1942:183). _Fayette_: Vandalia. _Gallatin_: Shawneetown (Cahn, _loc. cit._). _Hancock_: between Warsaw and Hamilton (Stejneger, _op. cit._:23). _Jackson_: Murphysboro. _Jasper_: Newton. _Marion_: Centralia. _Mason_: Havana. _Massac_: symbol on map. _Menard_: Petersburg. _Peoria_: Peoria. _Randolph_: Chester (Cahn, _loc. cit._). _Richland_: Olney (Stejneger, _loc. cit._). _Rock Island_: Rock Island. _St. Clair_: East St. Louis (Cahn, _loc. cit._). _Union_: (Cagle, 1942a:199). _White_: Carmi. _Whiteside_: Sterling (Cahn, _loc. cit._). _Woodford_: Mackinaw Creek (Garman _in_ Cahn, _loc. cit._).

INDIANA: _Carroll_: "near" Delphi (Agassiz, 1857:400). _Vigo_: Terre Haute (Blatchley, 1891:22).

IOWA: _Des Moines_: "near" Burlington (Agassiz, 1857:400). _Dubuque_: Mississippi River, 8 mi. S Dubuque (Goldsmith, 1945:447). _Lee_: Keokuk (Stejneger, 1944:23).

KANSAS: _Barber_: 5 mi. SE Lake City; Salt River, S of Aetna (Burt, 1935:321). _Cowley_: symbols on map (Smith, 1956:157). _Gray_: Arkansas River, 1 mi. W Cimarron (Clarke, 1956:215). _Leavenworth_: Missouri River, Fort Leavenworth (Brumwell, 1951:207-08). _McPherson_: Lindsborg (Breukelman and Smith, 1946:112). _Pratt_: State Fish Hatchery, "near" Pratt (Taylor, 1933:269). _Trego_: Wakeeney (Stejneger, 1944:24).

KENTUCKY: _Fleming_: Fox. _Rowan_: Triplett (Welter and Carr, 1939:130). _County unknown_: Ohio River (Funkhouser, 1925:71).

LOUISIANA: _De Soto_: Bayou Pierre (Strecker and Frierson, 1926:last page, no numbers).

MINNESOTA: _Houston_: Brownsville (Breckenridge, 1944:183). _Winona_: Homer (Stejneger, 1944:23).

MISSISSIPPI: _Warren_: Vicksburg (Cook, 1946:185).

MISSOURI: _Jackson_: Fry's Lake (Anderson, 1942:219). _Jefferson_: Meramec River (Boyer and Heinze, 1934:199). _County unknown_: Osage River (Agassiz, 1857:400).

NEBRASKA: _Franklin_: 1/2 mi. S Franklin; 1 mi. SE Naponee. _Furnas_: 4 mi. E Cambridge. _Lancaster_: Lincoln. _Nemaha_: Peru. _Thayer_: (Hudson, 1942:102). _Thomas_: (Smith, 1958:36).

NEW MEXICO: _San Miguel_: Conchos River above Conchos Dam (Shields and Lindeborg, 1956:120).

OHIO: _Brown_: mouth White Oak Creek, Higginsport. _Muskingum_: "near" Gaysport. _Pike_: Scioto River in Camp Creek, Newton and Scioto Twps.; Pike Lake. _Scioto_: Scioto River in Clay and Rush Twps.; Scioto River, Portsmouth; Scioto River, 3 mi. N Rushtown. _Tuscarawas_: Tuscarawas River, 2 mi. below Gnadenhutten; "near" Winfield. _Washington_: Dam No. 2, Muskingum River, northern edge of Marietta; Ohio River, 4 mi. SE Marietta (Conant, 1951:156, 264).

OKLAHOMA: _Alfalfa_: 6.5 mi. NE Ingersoll. _Comanche_: Camp Boulder, Wichita National Forest (Ortenburger and Freeman, 1930:188). _McCurtain_: _Pushmataha_: (Ortenburger, 1927:100).

PENNSYLVANIA: _Allegheny_: Neville Island, Ohio River below Pittsburgh (Atkinson, 1901:154). _Clarion_: Allegheny River at Foxburg (Netting, 1944:85).

?SOUTH DAKOTA: _County unknown_: Fort Mackenzie, Missouri River, 6-8 mi. below Cedar Island (Stejneger, 1944:15).

TENNESSEE: _Lake_: Mississippi River (Parker, 1948:29). _Pickett_: Obey River at Eagle Creek Ford (Shoup, Peyton and Gentry, 1941:75).

WISCONSIN: _Crawford_: _Pepin_: Mississippi River (Breckenridge, 1944:183; Pope and Dickinson, 1928:82).

=Trionyx muticus calvatus= Webb

Gulf Coast Smooth Softshell

Plate 47

_Trionyx muticus calvatus_ Webb, Univ. Kansas Publ. Mus. Nat. Hist., 11:519, 1 fig., 2 pls., August 14, 1959.

_Type._--Holotype, UI 31071, hatchling, sex undetermined, alcoholic; obtained from Pearl River, Roses Bluff, 14 miles northeast Jackson, Rankin County, Mississippi, by William F. Childers on August 25, 1952.

_Range._--Southeastern United States from the Florida Parishes of Louisiana eastward to the western end of the panhandle of Florida; rivers of the Gulf Coast drainage from the Escambia River drainage, Florida, westward to Louisiana and Mississippi including the Pearl River drainage. The eastern extent of geographic range is not known (see map, Fig. 22).

_Diagnosis._--Juvenal pattern of large circular spots, often ocellate; no stripes on dorsal surface of snout; pattern on dorsal surface of limbs of fine markings, not in contrast with ground color; pale postocular stripes having thick black borders approximately one half width of pale stripe on adult males.

_Description._--Plastral length of smallest hatchling, 3.0 centimeters (TU 17301); of largest male, 11.8 centimeters (KU 47118); of largest female, 18.0 centimeters (TU 13473).

Juvenal pattern of dusky, circular spots, some ocellate, lacking short lines and streaks; number of spots variable; some spots on carapace of hatchlings may have maximum diameter of three millimeters (TU 17301); pale rim of carapace having dusky, ragged, inner border; juvenal pattern on adult males absent or usually evident, at least posteriorly (TU 17306.1).

Dorsal surface of snout lacking pale stripes just in front of eyes; pale postocular stripe having thick, black borders on adult males, but narrower, dusky or blackish borders on juveniles and large females; lower border of postocular stripe usually in contact with dusky postlabial line; no other markings on side of head; pattern on dorsal surface of soft parts of body of closely approximated, fine markings that are not in contrast with ground color, over-all coloration grayish; occasionally few larger and more contrasting markings, especially on hind limbs and anteriolateral surface of forelimbs.

Underparts whitish, lacking markings, occasional black flecks or dusky marks posteriorly along ventral edge of carapace (TU 17306.3).

Surface of carapace smooth in adult males; large females lacking prominences posteriorly in center of carapace or in nuchal region; anterior edge of carapace smooth in both sexes, but occasionally having regularly spaced furrows or wrinkles on hatchlings.

_Comparisons._--_T. m. calvatus_ can be distinguished from _T. m. muticus_ by the absence of pale stripes on the snout just in front of the eyes, in having pale postocular stripes that have thick, black borders on adult males, and in having a juvenal pattern of large, circular spots that are often ocellate and three millimeters in diameter (no short lines).

_Remarks._--I have not seen specimens of _calvatus_ from the Tombigbee-Alabama river drainage; presumably Cook's record (1946:185) from Lowndes County, Mississippi, represents this subspecies.

It is still not certain that _calvatus_ occurs in streams that drain into Lake Pontchartrain, Louisiana; TU 17236 from the Amite River that lacks a diagnostic character is questionably referred to _calvatus_ (Webb, 1959:524). As mentioned previously _T. s. asper_ shows little evidence of intergradation with _T. spinifer_ in the Mississippi River drainage; _asper_ is present in streams of the Lake Pontchartrain drainage. _T. m. calvatus_ presumably shows a corresponding relationship with _T. m. muticus_ in the Mississippi River drainage. There are no specimens that indicate intergradation between _calvatus_ and _muticus_; _calvatus_ is expected in streams that drain into Lake Pontchartrain, Louisiana. Probably _calvatus_ occurs eastward in the Apalachicola drainage system.

_Specimens examined._--Total, 38 as follows: FLORIDA: _Escambia_: KU 47116, 50852, 50854-55, 50835-36, TU 13473, 16682, 17301, 17302 (2), Escambia River, 2 mi. E, 1 mi. N Century.

LOUISIANA: _East Baton Rouge_: TU 17236, Amite River, "near" Baton Rouge. _Washington_: TU 13795, Bogue Chitto River, Enon; TU 17303 (5), TU 17304 (4), Pearl River, "near" Varnado. _No data_: TU 17305.

MISSISSIPPI: _Lawrence_: KU 47117-19, TU 16956, USNM 7655, Pearl River within 4 mi. of Monticello; TU 17306 (4), Pearl River, 9 mi. S Monticello. _Marion_: USNM 95133-34, Pearl River, Columbia. _Perry_: MSC uncatalogued (3), 3 mi. SE New Augusta. _Rankin_: UI 31071, Pearl River, Roses Bluff, 14 mi. NE Jackson.

_Records in the literature._--MISSISSIPPI: _Forrest_: no data. _Jones_: Crawford Bridge. _Lowndes_: Columbus, Lake Park (Cook, 1946:185).

NATURAL HISTORY

Habitat

Most writers who describe the general habitat of soft-shelled turtles mention large rivers and streams having some current, and large permanent, quiet bodies of water having soft mud or sand bottoms, but note the general avoidance of temporary water. The impermanence of water in the ponds and "charcos" of headwaters of streams may preclude the presence of softshells from these otherwise suitable habitats. Seemingly, soft-shelled turtles are not restricted to particular local situations or microhabitats in a continuous aquatic environment as are some kinds of fish, which seem to be more or less confined to riffle areas or deep holes. Certain activities of softshells such as burying themselves in soft sand in shallow water or seeking crawfish and other food over a gravel-rock substrate or one that is débris-laden, are best carried on in different habitats. Repeated observations of turtles that are probably engaged in a specific activity in a restricted area may lead to erroneous general conclusions regarding the over-all preference for a specific habitat. Perhaps this accounts for Conant's statement (1951:156) that "In the lower portion of the Scioto River [Ohio] it appears that the present species [_muticus_] is abundant while _spinifer_ is almost entirely absent."

Cagle (1954:181) wrote that softshells "inhabit the extreme headwaters and smaller tributaries." Other statements in the literature indicate the variety in kinds of habitat. In Louisiana, Beyer (1900:44) mentioned _spinifer_ as abundant "in all inland waters, preferring, however, such bayous which have sloping and sandy banks upon which they are fond of sunning themselves." Viosca (1923:41) reported soft-shelled turtles as characteristic "of the large silt-bearing rivers ... such as the Pearl, Amite, Mississippi and Atchafalaya." Cagle and Chaney (1950:386) wrote that _spinifer_ in Louisiana was found in greatest abundance in streams having some current, but that individuals were also common in quiet areas; the habitats recorded were: False River--a lake of clear water supporting an abundance of submerged vegetation, the shallow ends having mats of water hyacinth; Lakes Iatt and Bistineau--cypress swamps having clear or muddy water; Caddo Lake--a large lake having a light oil film on the surface of the water, and vegetation toward the shore consisting of cattails, water lilies and water hyacinths, and along the bank of cypress and willow trees; Caddo Lake Spillway--muddy with swift current; Sabine River--swift current, traps set in quieter backwater areas or near cypress logs in river; Lacassine Refuge--traps set in inlets and coves of ship channel having vegetation of water hyacinth, alligator grass, and along bank, saw grass, cypress knees and snags. Stejneger (1944:59) reported _spinifer_ taken in barrow pits in Mississippi.

In Southern Illinois, Cagle (1942:160) recorded _spinifer_ in drainage ditches (normally having several feet of water and a lush growth of aquatic vegetation) that connect inland swamps to the Mississippi flood-plain but dry up periodically, and in Elkville Lake, an artificial lake having much aquatic vegetation in shallow areas (_op. cit._:157). Myers (1927:339) recorded a _spinifer_ from Indiana from a "tiny brook." In east-central Illinois P. W. Smith (1947:39) recorded _spinifer_ in mud-bottomed dredge ditches, lakes, ponds, small streams and rivers, whereas _muticus_ was found to prefer rivers having clean, sandy bottoms and was not taken from lakes or small streams. This restriction in habitat preference of _muticus_ is again emphasized by Smith and Minton (1957:346) who wrote that in Illinois and Indiana, _muticus_ "generally avoids lakes and minor streams." Weed (1923:48), however, recorded _muticus_ (and _spinifer_) from Meredosia Bay, Illinois, presumably a broad, shallow, muddy ox-bow lake of the Illinois River.

In Minnesota, _spinifer_ has been taken from the Mississippi River, which is described as fairly swift having a fluctuating water level, sandy islands, mud banks, a bed of pebbles and large boulders, and abundant crawfish (Breckenridge, 1955:5). In Michigan, Edgren (1942:180) recorded _spinifer_ from a "very small muck-bottomed lake." Evans and Roecker (1951:69) recorded _spinifer_ from Long Point, Lake Ontario, which is a "broad sand spit, straight on the lakeward side but irregular with wet flats and lagoons on the bayside."

In Kansas, Brumwell (1951:207-08) found "mostly young [_muticus_] ... in the old ponds left during flood stages of the Missouri River" ... and _spinifer_ occasionally ... "in the backwaters where stagnant ponds had been formed." In southcentral Kansas, Burt (1935:321) reported _muticus_ from "a sandbar at junction of a small creek and Medicine River" ... and ... a "shallow sand-bottomed, algae-filled pasture streamlet." The same author reported _spinifer_ from a "sand-bottomed prairie streamlet" ... and ... "an alga-filled pool near a stream." Burt (_loc. cit._) remarked that "No ecological differences in general habitat and field behavior of _mutica_ and _spinifer_ are evident in Kansas." Clarke (1958:21) observed _spinifer_ in Long Creek (Osage County, Kansas), which is a winding stream, characterized by numerous deep holes alternating with rocky riffles, and having high and wooded banks, and mostly mud bottom but occasional rock bottom.

Marr (1944:490) mentioned a _spinifer_ that was obtained on the bank of a small, mud-bottomed stream in the Texas panhandle, and Linsdale and Gressitt (1937:222) recorded _spinifer_ from irrigation canals in Baja California.

In southern Florida, _ferox_ occurs in all fresh-water habitats (Duellman and Schwartz, 1958:272). Carr (1940:107) reported _ferox_ as widely distributed in streams, lakes, big springs and canals. Judging from the numbers of turtles, "the larger canals in the Everglades must represent something like an optimum habitat" (Carr, 1952:417). Wright and Funkhouser (1915:119) wrote that in the Okefinokee Swamp, _ferox_ was especially abundant where the water is deep and the bottom soft, and the species was found wherever there were alligators. Deckert (1918:31) wrote that young _ferox_ were taken in springs and brooks near Jacksonville, Florida. Marchand (_in_ Carr, 1952:417-19) observed _ferox_ while water-goggling in Florida and noted that individuals buried themselves in deep water in white sand, mud or bubbling mud-sand springs, sometimes where there was vegetation overhead. Neill (1951:16) collected _ferox_ in marshes, "prairies," flood-plain lakes, lagoons, ox-bow lakes, mangrove swamps, rivers, creeks, calcareous spring runs, man-made lakes and lime sinks. The same author (_loc. cit._) reported taking _agassizi_ (= _asper_) in large muddy rivers, clear "blackwater" streams, calcareous spring runs, creeks, marshes, lagoons, ox-bow lakes, flood-plain lakes, lime sinks, man-made lakes, and smaller ponds. Crenshaw and Hopkins (1955:16), however, stated that in the area where _T. ferox_ and _T. spinifer asper_ overlap, "_asper_ is nearly always an inhabitant of fluviatile situations whereas _ferox_ is equally closely confined to non-fluviatile lakes and ponds"; in the region of sympatry, Schwartz (1956:8) reported _ferox_ from "a moderately fast, blackwater stream [Combahee River, South Carolina]."

Carr (1952:417) wrote that _ferox_ is not uncommon near the mouths of streams in brackish waters, where the tide must occasionally take it to sea, and cited Conant, who told of an individual found at sea in Bahaman waters; Carr (1940:25) listed _ferox_ as occasional in the marine-littoral, mangrove swamps, as did Neill (1951:16). Neill (1958:26-27) mentioned his observance of _ferox_ at the mouth of the Pithlachascotee River, Pasco County, Florida, where the water is sufficiently saline to favor the growth of oysters, and added that commercial fishermen had told him that these turtles are sometimes netted with loggerhead sea turtles (_Caretta_) in the Indian River. Neill (_op. cit._:5-6) also noted the presence of _ferox_ on Meritt Island, which supports an extensive saltwater herpetofauna, off the coast of Brevard County, Florida. Löding (1922:47) recorded _spinifer_ from Fig Island, Mobile County, Alabama, which is probably a marine or brackish water habitat. Cagle and Chaney (1950:386) obtained one _spinifer_ in a brackish marsh of the Sabine Wildlife Refuge, Louisiana; the poor trapping returns here (one _Trionyx_ and one _Pseudemys_ in 408 trap-hours) suggest that fresh-water species are not abundant in brackish habitats. Neill (1958:26-27) has summarized the occurrence of soft-shelled turtles in marine and brackish habitats.

My own observations indicate a variety of habitat preferences; the term "relatively clear" refers to waters in which visibility extends four to six inches below the surface at night using a head-light.

Individuals of _spinifer_ have been taken in large, deep rivers having a moderate to swift current, relatively clear water, mostly sand and clay bottoms, and emergent débris intermittent along the shoreline; the banks may be steep and of mud having a sparse growth of herbs (Black Warrior River, south of Tuscaloosa, Alabama), or of low extensive, sandy bars and beaches (Escambia River, near Century, Florida, Pl. 50, Fig. 1). A juvenile _spinifer_ was taken by hand among rocks in quiet water behind a rocky shoal in the large, deep-channeled Ocmulgee River (near Hawkinsville, Georgia). Several individuals of _spinifer_ were seen in the Flint River (near Bainbridge, Georgia), which had a swift current in a wide, deep channel, sandy or sand-silt banks, few brush piles along shore and many oölitic, submergent snags on an otherwise sandy bottom; the water was exceedingly clear and permitted water-goggling (this habitat has been obliterated by a dam on the Apalachicola River). A large female _spinifer_ was taken on a set line from the bottom of one of several deep holes (approximately seven feet) that were connected by shallow areas or riffles (near headwaters of Escambia River--Escambia Creek, Escambia County, Alabama). Two large females of _spinifer_ (one escaped) were taken on a trotline set in a large, deep, isolated barrow pit near the Escambia River (near Century, Florida); there was no aquatic vegetation, the water was slightly turbid, and the substrate was of a sand-silt or mud.

In Arkansas, _spinifer_ has been taken in large deep rivers having relatively clear water, a moderate current, steep banks four to 15 feet high, and a substrate of mud with few rocks (one taken on trotline, escaped; Black River, near Black Rock, Lawrence County). Two _spinifer_ were taken (trotline and hoop-net) from a smaller (approximately 50 feet wide) turbid river having a swift current, débris along the shoreline, and mud-gravel banks (Petit Jean Creek, Yell County). Several _spinifer_ and _muticus_ were taken from the White River (Marion County) having a sand-gravel or bed rock bottom and clear water; individuals were collected by hand in shallow water (approximately 3-1/2 feet deep) as they lay on the bottom in the main channel where the current was moderate to swift or in a quiet-water side channel having submergent vegetation.

Lake Texoma, an impoundment on the Red River, having a fluctuating water level with no permanent stand of aquatic vegetation, a mud-rock or sand-silt bottom, and turbid water (Pl. 49, Fig. 1) is a suitable habitat for _spinifer_ and _muticus_. _T. spinifer_ is found in large rivers having relatively clear water, moderate currents, emergent logs and débris, and mud or sand banks (Little River, McCurtain County, Oklahoma, Pl. 48, Fig. 1), or small, shallow, turbid creeks having sand-gravel channels of pools connected by riffle areas (Mayhew Creek, Choctaw County, Oklahoma).

Three _spinifer_ were taken from the Llano River (near Llano, Texas) in a period of low water level in hoop-nets set in a large quiet-water pond about four feet deep and having patches of rushes encroaching into the water from the shore. The river bed of sand, gravel and large boulders consisted of narrower, swift-water channels, small pools and riffles, and large ponds.

Individuals of _T. s. emoryi_ have been taken in large ponds having little or no current, turbid, deep water, and clay or sand-gravel banks (Río Purificación, Padilla, Tamaulipas). Two _emoryi_ were collected from a large pond (Río Sabinas, near Sabinas, Coahuila), which was connected to an adjoining one by riffle areas and had little or no current, relatively clear, greenish water, clay or mud banks, a sand-gravel bottom, and was flanked by brush and large cypress trees. A few _emoryi_ were trapped in hoop-nets that were set in the Río Mesquites, a stream in central Coahuila approximately 20 feet wide and six feet deep, flanked by dense stands of _Phragmites_, and having a moderate current, relatively clear, pea-green water and a mud-sand substrate with some gravel; the stream enlarged in some places to form quiet-water coves (Pl. 48, Fig. 2). One adult male _emoryi_ was taken from a crystal-clear, dendritic, pond (El Mojarral, near Cuatro Ciénegas, Coahuila), having shallow areas averaging about two feet but several deep holes--in one of these at the west end of the pond the water was being emitted under pressure from an underwater cavern and "bubbling" at the surface; the vegetation consisted of scattered patches of water-lilies and stonewort; the bottom was a soft mud-marl, and in some places was carpeted with shells of small gastropods. This habitat corresponds to that of the type locality of _T. ater_ (Pl. 49, Fig. 2); see description in Webb and Legler (1960:26). The water of the ponds is warm; at 8 p. m. on July 31, 1959, the temperature of the water at the type locality of _ater_ was 29° C., and the air was 27° C.

An immature female _spinifer_ was taken on a trotline in a swift, clear, cold-water habitat having mud banks and an abundance of brush piles (Little Tennessee River, Monroe County, Tennessee). _T. spinifer_ occurs also in large ox-bow lakes having relatively clear water, extensive mats of submerged vegetation, a soft mud bottom, and several emergent stumps and fallen logs (Lake Concordia, Concordia Parish, Louisiana); alligator grass and cypress trees encroached to the shoreline.

Locality data of some individuals of _spinifer_, _hartwegi_, _asper_, _pallidus_ and _emoryi_ that were examined indicated that turtles were captured in ponds, bayous, sloughs, lakes, impoundments, rivers and creeks, indicating habitation of essentially all permanent waters.

A juvenile of _hartwegi_ was seen by Mr. Wendell L. Minckley on a gravel bar jutting into a small, shallow creek having a mud-gravel bottom (Carnahan Creek, Pottawatomie County, Kansas); the impounding of the Big Blue River by the Turtle Creek Dam will obliterate this habitat. Mr. J. Knox Jones, Jr. reported seeing a large softshell in a narrow, shallow, clear sandy creek in Holt County, Nebraska.

_T. s. emoryi_ occurs in large rivers having generally turbid waters, a moderate to swift current and mud or sand bottoms such as the Río Grande; this habitat corresponds to that of large rivers in the western parts of the range of _T. s. pallidus_ (Red and Washita) and _T. s. hartwegi_ (Canadian and Cimarron). These last-named rivers, in periods of low water level, often have shallow, clear, flowing water in parts of the river bed. _T. s. emoryi_ has also been taken from small creeks having bottoms of rocks and large boulders (Black River Village, Eddy County, New Mexico; field notes of Sydney Anderson and Kenneth Shain, June 12-14, 1958).

I received a hatchling _T. s. guadalupensis_ that was obtained in a clear, shallow-water stream (Hondo Creek, Bandera County, Texas, on April 12, 1958). The larger streams and rivers known to be inhabited by _guadalupensis_ are generally clear having greenish-tinted waters. The geographic distribution of _guadalupensis_ indicates that that subspecies occurs principally in those waters that drain the limestone-mantled, Edward's Plateau off the Balcones Escarpment; the headwaters are characterized by clear, calcareous streams having occasional travertine deposits. It is probably this type of habitat to which Agassiz's statement (1857:408) of "clear, bold and rocky streams" refers.

There are a few specimens whose locality data indicate a tolerance of brackish-water habitats. An adult male _spinifer_ was obtained at Delacroix Island, St. Bernard Parish, Louisiana, a locality said to have exceedingly brackish waters (Dr. George H. Bick, St. Mary's College, Notre Dame, Indiana); this adult male (TU 16170) is unique in having a mottled and blotched pattern. Another adult male (_spinifer_, TU 16071) was obtained in shallow water in Lake Pontchartrain at the mouth of Tchefuncta Creek; the salinity at the time of capture was recorded as 1.7 (datum from Dr. Royal D. Suttkus, Tulane University), indicating only slightly brackish water. Two _spinifer_ (USNM 100409-10) and one _muticus_ (USNM 100406) were taken at Berwick Bay, near Morgan City, St. Mary's Parish, Louisiana; the waters at this locality are probably brackish. The tolerance of brackish waters doubtless facilitates the dispersal of these turtles along coastal marshes and swamps, and into adjacent drainage systems. The greater number of records in the literature pertaining to _ferox_ suggest that this species may be more tolerant of brackish and marine waters than are _spinifer_ or _muticus_.

In summary, _T. ferox_ occurs in all fresh-water habitats, but chiefly in lentic habitats in the northern part of its range where it and _T. s. asper_ are sympatric. _T. ferox_ possibly is more tolerant of brackish and marine waters than are the subspecies of _spinifer_ and _muticus_.

The subspecies of _T. spinifer_ occur in all fresh-water habitats. In the southern part of the geographic range, which overlaps that of _T. ferox_, _T. s. asper_ occurs principally in running-water habitats. _T. s. pallidus_ and _T. s. asper_ are tolerant of brackish-water habitats. _T. s. guadalupensis_, known at present only from rivers and streams, occurs principally in river systems that drain the Edward's Plateau of southcentral Texas. _T. ater_ is confined to crystal-clear ponds in central Coahuila.

The subspecies _muticus_ occurs in large rivers and streams throughout its geographic range, but is known from lakes and impoundments principally in the southern part of its range (the northernmost record is from Reelfoot Lake, Obion County, Tennessee); there is only one record of _muticus_ from a small, shallow, headwater creek (Reno County, Kansas), and only one from a lentic habitat (Meredosia Bay, Illinois) in the northern part of its range. _T. muticus calvatus_ is known at present only from rivers and streams.

The seemingly greater restriction of _muticus_ to running-water habitats suggests less vagility than in _spinifer_ (Netting, 1944:86).

Size and coloration are adaptations to habitat. Soft-shelled turtles of large size are best adapted to mesic, essentially continuous swampy or marshy habitats, whereas small size is an adaptation to less continuous, semi-isolated habitats. A turtle of the maximum size attained by _ferox_ in the habitat of _emoryi_ would, in a general way, probably be more conspicuous and exposed to its enemies, both in the aquatic environment and during overland excursions; perhaps the kind and amount of food would be insufficient. In any event, small size is correlated with the more arid habitats of the southwest, and large size with mesic ones in the southeast. _T. ferox_, the largest species, and the smallest population of _T. spinifer_ (resembling _muticus_) both occur in the southernmost part of the range of the genus. This situation does not support the corollary of Bergmann's Rule, that pertains to some groups of terrestrial reptiles, in which those subspecies occurring farther north, or in cooler climates during their season of activity, tend to be smaller.

Within the species _spinifer_, the _emoryi_ group of subspecies are pallid having whitish dots on the carapace and lack extensive black pigmentation; these features seem to confer protective coloration on the inhabitants of arid, essentially sandy or muddy habitats having sluggish, turbid waters, whereas the more contrasting patterns of the _spinifer_ group of subspecies eastward seem more suited to existence in clearer, swifter waters.

The occurrence of the two clines, _spinifer-hartwegi_ and _pallidus-guadalupensis_, in the species _spinifer_ are notable in that the former occurs mostly in one large continuous drainage system, that of the Mississippi, and shows no sharp break in the one character distinguishing the two subspecies whereas populations composing the _pallidus-guadalupensis_ cline are separated into several river drainages, and show a relatively sharp break in several characters at the Brazos-Colorado river divide. This situation seemingly supports the thesis that clines are maintained by some sort of parallel gradient in ecological or geological conditions. It is notable that streams draining the Edward's Plateau (inhabited by _guadalupensis_) differ in quantity (more) and quality (especially CO_{3}^{--}, Ca^{++}, and Mg^{++} ions) of their solutes, and probably pH (higher) from those farther east (Hubbs, 1957:102). The gross difference in habitats mentioned above (sandy, turbid, sluggish streams in the west _vs._ clear, swift streams in the east) may affect the differentiation recognizable in the _spinifer-hartwegi_ cline.

Daily and Seasonal Activity

_Diurnal Habits_

Softshells bask on débris in the water or on banks close to the water; basking presumably raises the bodily temperature. In general in the southeastern and southwestern United States, I have seen softshells basking only rarely but once saw six at one time close together on logs in Bowie Creek, Hattiesburg, Mississippi (species undetermined). Surface (1908:122) saw _spinifer_ in rows on rocks or logs in tributaries of the Ohio River. Duellman and Schwartz (1958:271-72) stated that _ferox_ basks on banks or beds of aquatic vegetation. Deckert (1918:31) mentioned large _ferox_ "sunning in shallow water at edge of pond." Minton (1944:447) wrote that _muticus_ and _spinifer_ sun on steep mud banks (Wabash River). Cahn (1937:180) stated that _muticus_ (in Illinois) basks on banks at the water's edge but seldom on logs, and suggests that _muticus_ is less prone to leave the water than _spinifer_. According to Carr (1952:438), _muticus_ never basks on logs or rocks. In Ohio, Conant (1951:159) mentioned _spinifer_ as occasionally basking upon a log or rock, or sometimes on steep clay banks of streams. On banks, quick escape is facilitated by directing the head toward the water, thus eliminating the time that it would take to turn around on land (Conant, _loc. cit._; Newman, 1906:129). Evermann and Clark (1920:593) mentioned _spinifer_ as basking on sandy or grassy shores, and large boulders. Muller (1921:181) wrote that _muticus_ basks four to ten feet from the water's edge on gently sloping sand and mud shores of small islands in the Mississippi River (near Fairport, Iowa). Muller stated that basking usually occurs in the morning, up until 2 p. m., and that beaches with a northern exposure were preferred; he observed 37 turtles within a 50-foot stretch of beach. In captivity, hatchlings bask on wire-mesh supports.

I have frequently observed softshells floating at the surface of the water, a habit previously mentioned by Surface (1908:122) and Pope (1949:305, 311). Individuals of _Pseudemys_ and, to a lesser extent, _Graptemys_ also float at the surface; those kinds of turtles and softshells at least, often appear at the surface of the water, seemingly as a result of an inquisitiveness, following repeated disturbances that cause submergence.

Newman (1906:131) described the active pursuit of food: "They crawl or swim along the bottom, thrusting their snouts under stones and into masses of aquatic vegetation, occasionally snapping up a crayfish or larva that they have succeeded in dislodging. They do not tear up their food, but swallow it whole, using the forefeet to assist in forcing it down." Surface (1908:123) suggested that softshells may feed "upon insects which may be found floating on the water," and I have had captives take insects from the surface of the water. Carr (1940:107) also wrote that _ferox_ and numerous gars in the Tamiami Canal, often at the mouths of the tributary ditches, snap at each other furiously as floating bits of food are washed in from the Everglades. Another habit that has been mentioned as an aid in acquiring food (Breckenridge, 1944:186; Conant, 1951:156; Hudson, 1942:101) is burrowing just below the surface in a soft bottom in shallow water, to ambush passing fish, or other food. Presumably all kinds of softshells do this in both shallow and deep water of lakes or rivers having a suitable substrate; _spinifer_ and _muticus_ have been reported to burrow in shallow waters (no observations in deep water) by Agassiz (1857:333), Cahn (1937:180, 189), Conant (1951:159) and Weed (1923:48). Marchand (_in_ Carr, 1952:417-19) noted that _ferox_ burrows in deep water, and mentioned that in areas of bare white sand a group of fish invariably surrounds them, and one can locate buried softshells by observing these particular schools of fish. No mention was made of the turtles attempting to catch the fish. Other associations of soft-shelled turtles and fish have been described. Kirtland (_in_ DeKay, 1842:7) observed several large bass that closely followed large numbers of turtles floating at the surface. Newman (1906:131) reported the observations of fishermen in Lake Maxinkuckee that large-mouth black bass stay not far away from swimming softshells; the same author also mentioned the observations of Jacob Reighard, who suggested that bass may be feeding upon minnows that he noticed following softshells. Seemingly some sort of commensalistic relationship exists whereby fish acquire food that is dislodged by grubbing and scurrying of softshells. Probably food is pursued on occasion from a buried position, but this habit probably is not executed specifically for obtaining food. Newman (_op. cit._:129) was of the opinion that burrowing in shallow water is a habit to facilitate "warming up."

Marchand (_loc. cit._) also wrote of other notable underwater observations on _ferox_ in Florida. He commented on this turtle's inquisitiveness in deep water and unconcern upon being touched or even upon being handled to some degree. Calf-deep in soft mud, he noted a turtle that "emerged from the mud of the bottom, headed up toward shore, circled, and when about three feet above the bottom dived suddenly and completely disappeared." Marchand wrote that some areas on the bottom (Crystal Springs), which are rooted up by the burrowing of softshells, are bare and soft, and assume a characteristic, easily recognized, appearance.

Cahn (1937:180, 189) stated that the burrowing process consists of "flipping" the loose sand or silt over the back, whereas Conant (1951:159) described the process as a rapid lateral movement of the body. My observations of captives agree essentially with Conant's observations. The initial movement, directed at a slight angle, is principally with the forelegs although complemented by lateral movements of the body. When the turtle is approximately half buried, it makes rapid lateral movements of the body, which completely bury the turtle and orient its body in a horizontal position.

_Behavior and Adaptations_

Some characteristics of softshells that are often mentioned in the literature are: extreme shyness or wariness, ferociousness as captives, dazzling speed and agility on land and in water, and great dependence on aquatic environment. Certainly they are wary; and this wariness may account, in part, for the scarcity of observations of basking, and statements attesting to their great speed on land. To my mind, their reported ferociousness and savage disposition as captives is overrated; of the many softshells that I have collected, only a few attempted to bite. The extensibility of their long neck does warrant more careful handling than needs to be employed with other species. Holbrook (_in_ Hay, 1892:145) even wrote that they "will sometime leap up and give a loud hiss," and Newman (1906:130) wrote that "they hiss violently and thrust out the head." Wright and Funkhouser (1915:120) reported a captive _ferox_ that "could jump forward practically its own length." I have been bitten by individuals of _Kinosternon_, _Sternothaerus_, _Pseudemys_ and _Graptemys_, and cannot support the contention that softshells are more prone to bite than those species, a view shared by LeConte (_in_ DeKay, 1842:7); many softshells on initial capture will tend to withdraw the head completely for a short time. Newman (_loc. cit._) also wrote that recently captured specimens exude a thick, yellow, semi-fluid resembling yolk of an egg from the inguinal glands; the substance, however, is odorless but "undoubtedly homologous with the emission of the inguinal glands of the musk and snapping tortoises." Perhaps there is a difference in aggressiveness associated with geographic location, the age of the turtle or individual temperament.

Smith (1956:159), referring to _muticus_, wrote that they are the best swimmers of all fresh-water turtles, and perhaps of any turtles. Corresponding statements of other authors attesting to their speed and agility (including _spinifer_ and _ferox_) in water and on land are based principally on the published comments of Muller (1921:181), who observed that females disturbed while laying eggs "about fifty feet from water ... covered the distance faster than a man can run." Cahn (1937:180) also stated that _muticus_ on a "level, unobstructed sand beach ... can outrun a man," and (_op. cit._:181) can "capture fish with ease"; Cahn supported the latter statement by relating his observation of a _muticus_ that captured a small brook trout in a large tank. Smith (_op. cit._:162) wrote that _spinifer_ is "said to overtake bass." Doubtless they are good swimmers and they do scurry rapidly on land.

Published statements relating to the strictly aquatic existence of softshells especially _muticus_, are based on recognition of "its drastic adaptations to aquatic existence" (Carr, 1952:428); these adaptations presumably include pharyngeal respiration and the marked depression of body form. Pharyngeal respiration was demonstrated for _muticus_ and _spinifer_ (Gage, 1884; Gage and Gage, 1886), and was considered the principal type of aquatic respiration (some dermal and some cloacal) in _Trionyx spinifer asper_ by Dunson (1960). Cloacal bursae (anal respiration) are lacking in trionychids (Smith and James, 1955:88). Accessory pharyngeal respiration is meaningful in light of the information furnished by Agassiz (1857:282-83), who found that _Trionyx_ has a smaller lung capacity (weight of body in ounces/capacity of lungs in cubic inches = 16.9) than do some other genera (_Pseudemys_, 2.8; _Testudo_, 2.7; _Terrapene_, 1.1); corresponding values for more aquatic species were _Chelydra_, 9.3 and _Kinosternon_, 16.0. Cahn (1937:181), however, wrote that he has demonstrated pharyngeal respiration in individuals of _Pseudemys_, _Chrysemys_ and _Sternothaerus_, and Allen and Neill (1950:13) suggested that it occurs in _Macroclemys_. More conclusive data are required to detect a positive correlation between small lung capacity, pharyngeal respiration, and degree of restriction to an aquatic habitat.

The depressed, soft-margined carapace of softshells has been mentioned as an adaptation to facilitate burrowing in soft sand or mud, and more suited for concealment than for speed in aquatic locomotion (Carr, 1952:429; Smith, 1956:162). Nielsen (1951:264-65), commented that in various lotic invertebrates, dorsoventral flattening of the body was no commoner than in lentic invertebrates; he wrote that a dorsoventral flattening is a disadvantage to an animal in a strong current and is an adaptation "probably ... not to withstand the current directly, but to avoid it by seeking shelter in narrow crevices." Probably another aid to concealment, mentioned by Williams and McDowell (1952:272), is the plastral hinge.

Concealment of softshells is not enhanced by growths of algae on the carapace. Proctor (1958:637-38) reported that the common, epizoöphytic alga of chelonians, _Basicladia_, has never been reported from _Trionyx_; the same author recorded a large amount of filamentous algae, principally _Stigeoclonium_, but the algae could be easily wiped from the turtle, and Vinyard (1955:64) recorded an alga, _Dermatophyton radians_, attached to the skin of the legs of _Trionyx_. I noted a small patch of greenish scum growing near the insertion of the neck on a softshell (_spinifer_ from Lake Texoma); cursory examination by Dr. R. H. Thompson, disclosed one of the colonial ciliate protozoans (resembling _Opercularia_) with enmeshed green or blue-green algae. Evermann and Clark (1920:592) mention a _spinifer_ from Lake Maxinkuckee, Indiana, having a growth of _Opercularia_, covering the plastron.

_Movement_

The reported proclivity of softshells for a strictly aquatic existence has been over-emphasized; they are no more confined to aquatic habitats than some chelydrids (including kinosternids). In fact, there is a general parallel in habits between members of the two families, namely, a tendency toward a bottom-dwelling existence, and a burrowing habit. The alligator snapping turtle (_Macroclemys_) is probably the most aquatic fresh-water turtle in the United States. The common snapping turtle and some kinosternids are known to migrate overland. Kinosternids and trionychids bask frequently, and trionychids have been observed moving overland. Cox (1894:50) reported a _spinifer_ attempting to climb a narrowly-stepped, 12-foot dam on Mud Creek at Ravenna, Nebraska; the turtle failed after repeated struggles, once reaching a height four inches shy of the brim before tumbling back into the water. Duellman and Schwartz (1958:271) commented that adults of _ferox_ are often seen on roads bordering canals, and informants have told me verbally of similar observations. Conant (1930:61) reported an individual of _ferox_ that was "... walking across the main street in Venice [Sarasota County, Florida]." Softshells will travel overland in search for suitable nesting sites; Newman (1906:130) wrote that _spinifer_ will climb "steep railway embankments with considerable ease, in order to reach a sand pit some fifty yards from the water."

From an analysis of species-composition of large reservoirs and lakes and their adjacent smaller ponds in southern Illinois, Cagle (1942:162) concluded that softshells "travel overland far less often than do ..." other species, but that they are "probably the first to move as the water level falls." On the basis of further observations in the same region, Cagle (1944:15) wrote that softshells rarely move overland, and once trapped in a pool of water, they bury themselves and remain there. He related instances of several individuals having been dug from dried mud where the last remnants of a water pool had evaporated and he concluded that the home range is probably confined to one body of water. That fluctuations in water level affect the movement of softshells is suggested by Mr. William E. Brode's comment that a commercial fisherman trapped numerous softshells in the Pearl River, south of Monticello, Mississippi, in unbaited hoop-nets in late May and June when the water level was receding after heavy rains.

The meager data available concerning the aquatic movements of softshells indicate that individuals wander but little. Breckenridge (1955:6, table 1) found that among 30 recaptured turtles that had been marked, the greatest distance traveled was 600 yards over a two-year interval; after a three-month interval one originally captured 30 miles distant, moved only 200 yards. The statement of a professional turtle trapper mentioned by Breckenridge (_loc. cit._) and data previously presented (see page 436), to the effect that over-trapping results in increasingly diminished returns, tends to support the idea that there is little aquatic movement in soft-shelled turtles.

Breckenridge (_loc. cit._) mentioned methods of marking softshells and found that notching the edge of the carapace with a leather punch was satisfactory; the notches healed but were discernible as shallow sinuses. The same author mentioned a tattooing device (mentioned also by Cagle, 1939:171), but no turtles so marked were ever recognized as recovered. Tagging with a radioactive isotope and detection with suitable instruments should prove applicable to turtles (see Karlstrom, 1957).

_Nocturnal Habits_

Anderson (1958:212) wrote that hatchlings (_muticus_) leave nests within the first three hours after sunset, and are active on the surface of the sand at night. Muller (1921:183) reported hatchlings (_muticus_) leaving nests at night or early in the morning. Lagler (1954) stated that _spinifer_ is nocturnal. To my knowledge there are no other published statements concerning nocturnal activity of soft-shelled turtles. I have noted them at night on only four different occasions. In two instances (Clear Fork Brazos River, Texas, and Lake Concordia, Louisiana), the turtles were resting immediately below the surface of the water on submerged branches, as one would expect _Pseudemys_ and _Graptemys_ to do. Another individual was seen swimming near the surface (Ocmulgee River, 1-1/2 mi. S Jacksonville, Georgia); this observation possibly represents nocturnal activity, or inquisitiveness owing to the disturbances caused by the motor of the boat and/or our head lights. A final observation tends to support the view of nocturnal habits. My field notes record at least four softshells collected by hand, and a few other seen in a shallow (approximately four feet deep), quiet, clear water side channel of the White River (Cotter, Arkansas); the turtles were seen resting and slowly moving on the bottom or swimming.

_Seasonal Occurrence_

The length of the season of activity increases with decrease in latitude. Aquatic species in general have longer periods of activity than terrestrial species at the same northern temperate latitudes. The southernmost populations of all species of softshells may be active throughout the year, assuming temperature to be the limiting factor.

There are few published statements relative to the length of the annual period of activity; all records refer to _spinifer_. In Lake Maxinkuckee, northern Indiana, Newman (1906:128) wrote that individuals were first seen in early April on the lake shore in a weak condition with neck and legs extended, and were easily captured. Lesueur (1827:262) wrote that _spinifer_ in Indiana appears toward the end of April. Observations of Evermann and Clark (1920:592) in Lake Maxinkuckee, and Butler (1894:224) in east central Indiana concurred in finding that of all kinds of turtles there, softshells appeared last in spring and disappeared first in fall. Evermann and Clark found small softshells, benumbed or dead, along the shore as early as March 18 and also late in fall. The earliest observation for large softshells was April 29, and the latest was September 7; Butler found that these turtles rarely appear before April 15 and sometimes not until May 1. Cahn (1937:191) stated that softshells in Illinois hibernate toward the end of October and emerge in May or the latter part of April; the same author mentioned that in southern Illinois the species might remain sluggishly active all winter. In Ohio, Conant (1951:160) wrote that individuals were collected every month from March to October, and one was even taken in December, 1929, in northwestern Ohio. Wright (1919:8) mentioned observing softshells on April 20 and September 20 (presumably these were the earliest and latest observations of them) in Monroe and Wayne counties, New York. Blatchley (1891:34) listed dates of early and late activity as March 19 and December 11 for Vigo County, Indiana. Webster (1936:22) recorded the earliest and latest dates of collection of _spinifer_ in central Oklahoma as June 10 and November 8.

Moore and Rigney (1942:80) found an individual of _muticus_ under six inches of ice in water about one foot deep on January 31, 1940 (Cimarron River, Payne County, Oklahoma).

The published information suggests that the length of the normal annual period of activity of _spinifer_ in latitudes of about 40° and 43° is approximately five months, from April into September, depending upon the weather. There are numerous published statements to the effect that the period of hibernation is passed under a shallow covering of mud in deep water. Evermann and Clark (_op. cit._: 593) found a softshell (presumably in a quiescent state) on September 6 that was "buried up to its eyes in mud at the edge of Lost Lake." Softshells possibly hibernate in shallow water or in soft mud flats. Conant (_loc. cit._) found that captives would not hibernate in a pond in a zoo having a bottom of leaves.

Food Habits

Previous authors, most of whom allude to published statements preceding their own, characterize soft-shelled turtles as carnivorous and mention such food items as crawfish, insects, worms, snails, clams, frogs, tadpoles, fish, and occasional vegetable matter. Stockwell (1878:403) wrote that the relative lengths of portions of the digestive tract indicate "a purely carnivorous diet."

In an examination of the contents of 11 stomachs of _spinifer_ from Michigan, Lagler (1943:304) found that crawfish (47%) and insects (52%), principally burrowing mayfly naiads (_Hexagenia_), and dragonfly naiads, comprised the bulk of the diet with cryptogams, vegetable débris, snails and fish remains present in small amounts. Breckenridge (1944:186) wrote that 18 specimens of _spinifer_ in Minnesota contained 44 per cent crawfish, 29 per cent aquatic insects, 8 per cent fish, and 19 per cent unidentified material. Surface (1908:123) found crawfish in the only two stomachs of specimens he examined from Pennsylvania. Penn (1950) summarized the results of those authors, and estimated that crawfishes comprised 58 per cent (46% by volume) of the diet of softshells. In Indiana, three stomachs examined by Newman (1906:131) in late June contained: 1) nine crawfish, 2) four crawfish, 22 dragonfly naiads, 3) nine dragonfly naiads, few plant buds. Neill (1951a:765) found crawfishes in the stomachs of five _spinifer_ from the Savannah River, Georgia. Evermann and Clark (1920:595) wrote that _spinifer_ in Lake Maxinkuckee feeds principally on crawfishes. Shockley (1949:257) mentioned bottom organisms and small fishes as food. Clark and Southall (1920:16) stated that "Its principal food, to judge from a few specimens examined, consists of crayfishes."

Cahn (1937:183) wrote that the food of _muticus_ in Illinois consists principally of crawfish, fish, frogs, tadpoles, larger insect larvae and nymphs, and aquatic mollusks. The kinds of fish eaten were _Notropis heterolepis_, _N. spilopterus_, _N. hudsonius_, _Lepomis machrochirus_, _Morone chrysops_, _Perca flavescens_, _Catostomus commersonnii_, and _Hypentelium nigricans_; Cahn (_loc. cit._) also stated that the mollusks eaten by _muticus_ are both gastropods and small, thin-shelled bivalves. In regard to the feeding habits of _spinifer_ in Illinois, Cahn (_op. cit._:193) listed the following items in decreasing order of abundance as revealed by examinations of stomachs: crawfish, minnows, fry of larger fish, frogs, tadpoles, earthworms, insects (often beetles), and mollusca (_Pisidium_, _Viviparus_, planorbids). The kinds of fish mentioned were: _Notropis heterodon_, _N. heterolepis_, _N. hudsonius_, _Catostomus commersonnii_, _Lepomis humilis_, _L. macrochirus_, _Semotilus atromaculatus_, _Notemigonus crysoleucas_, _Umbra limi_, and _Micropterus salmoides_. Cahn (_loc. cit._) also found the remains of a six-inch brook trout (_Salvelinus_) in the stomach of a 13-inch _spinifer_ from Wisconsin.

Agassiz (1857:399) found larvae of neuropterous insects in the stomach of one specimen of _muticus_, and fragments of _Anodonta_ and _Paludina_ (= _Campeloma_) in the stomach of one _ferox_. The expanded crushing surfaces of the jaws in some large individuals of _ferox_ may be an adaptation to mollusc-feeding (Schmidt and Inger, 1957:36). Surface (1908:123) found _spinifer_ to have fragments of beetles in one of two specimens examined, and large quantities of corn in another from Ohio. Webb and Legler (1960:27) reported 23 chrysomelid beetle larvae (_Donacia_) in one specimen of _T. ater_. Evermann and Clark (1920:595) reported several _spinifer_ taken on hooks baited with grasshoppers in water 14 feet deep in Lake Maxinkuckee, Indiana. Hay (1892:144) wrote of _muticus_ that "If there are potatoes growing near the water the turtles find their way to them and devour the stems, of which they are very fond." Wright and Funkhouser (1915:123) stated that young _ferox_ in the Okefinokee Swamp feed on fish and frogs, and according to the natives, larger specimens take waterfowl, a statement that Smith (1956:159) was probably reiterating when he mentioned that the diet included "perhaps young birds." Parker (1939:88) wrote that of two _spinifer_ from Reelfoot Lake, Tennessee, one contained coleopteran remains, and the other an aquatic beetle and two large tipulid larvae. Wied-Neuwied (1865:54) wrote that Lesueur found worms, snails, remains of _Paludina_ (= _Campeloma_), fruits and even hard nuts in stomachs of _muticus_.

Holbrook (_in_ Hay, 1892:145) mentioned that _spinifer_ feeds on fish and such reptiles as it can secure. There are no published statements known to me that report reptiles in the diet of American softshells. Carr (1952:425) erroneously cited Strecker (1927:9) and attributed "a young lined snake" to the diet of _T. s. emoryi_; Strecker, however, referred to _Kinosternon flavescens_. In conjunction with raising softshells on turtle farms, Mitsukuri (1905:261) mentioned that first and second year-old turtles (_Trionyx sinensis_) must be transferred to separate ponds or they will be eaten by adults; perhaps corresponding cannibalistic tendencies exist in confined, natural habitats in American softshells.

Captives eat essentially the same things that free-living individuals do, plus scraps of meat (Strecker, 1927:9; Gloyd, 1928:135; Pope, 1949; Conant, 1951:156, 160). Lagler (1943:303) mentioned a young _spinifer_ that fed on water fleas (_Daphnia_) and canned fish. Conant (_op. cit._:160) wrote that no captive was observed to take vegetable matter.

Food, mostly in intestines, of two adult females of _T. s. emoryi_ collected on June 12-14, 1959, from the Río Grande at Lajitas, Brewster County, Texas, was examined. One female, KU 51961, contained little food and mostly plant fragments; because the stomach or intestine was not full of plant fragments, this food probably was ingested incidentally to the few insects present. Another female, KU 51955, contained insects, which were identified by Dr. George W. Byers, Department of Entomology, University of Kansas, as follows: 1) Coleoptera, Dryopidae, genus _Helichus_, most numerous, 350 to 400 individuals; 2) Coleoptera, Scarabaeidae, genus _Phyllophaga_, one individual; 3) Odonata, Coenagrionidae, fragments, probably one individual; 4) Hymenoptera, Sphecidae, subfamily Bembicinae, one individual; 5) Ephemeroptera; fragments of naiad; and 6) a few plant seeds, pieces of slender roots, weed stems and a couple of fragments of tree bark. The scarab and wasp probably fell into the water and were eaten.

TABLE 6. Kinds of Insects Found in Stomachs and Intestines of 11 Specimens of Trionyx m. muticus (Eight Adult Males and Three Immature Females, 9.0 to 12.5 cm. in Plastral Length) From Douglas County, Kansas. Frequency of Occurrence (Approximate Number of Individual Insects/Number of Stomachs in Which Found) Is Given for Each Item Listed. Fragments of Insects Represent Adults Unless Otherwise Noted.

==========================================================+=========== FOOD ITEM | Frequency ----------------------------------------------------------+----------- Orthoptera | Locustidae | 1 | Ephemeroptera | Unknown (naiad) | 1 | Odonata | Anisoptera (naiad) | 3/3 Zygoptera (naiad) | 4/2 | Plecoptera | Unknown (naiad) | 2/1 | Homoptera | Cicadellidae | 20/7 | Hemiptera | Lygaeidae | 1 | Neuroptera | Corydalidae (_Corydalis_ larva) | 1 | Trichoptera | Hydropsychidae? (incl. 18 larvae and 4 pupae) | 23/9 Unknown (incl. 1 larva) | 4/4 | Lepidoptera | Noctuidae? (larvae) | 2/1 Pyralidoidea (larva) | 1 Unknown | 1 | Coleoptera | Carabidae (incl. 1 larva) | 3/3 Cerambycidae? | 1 Chrysomelidae | 1 Cicindelidae (larva) | 1 Elateridae (larva) | 1 Hydrophilidae? (larvae) | 4/2 Scarabaeidae (incl. _Phyllophaga_) | 9/6 | Diptera | Anthomyiidae | 1 Asilidae | 1 Bibionidae (_Bibio_) | 5/2 Calliphoridae (puparium) | 1 Empididae | 1 Mycetophilidae | 1 Tipulidae (incl. _Tipula bicornis_ and _T. triplex_?) | 9/4 Unknown (5 muscoid, 3 acalyptrate, and 1 cyclorrhaphous | types) | 9/4 | Hymenoptera | Apoidea | 1 Formicidae (incl. _Camponotus_) | 11/4 Ichneumonidae (one questionable) | 4/3 Tenthredinidae | 1 Unknown (small wasps) | 3/2 ----------------------------------------------------------+-----------

Food from the digestive tracts of 11 specimens of _T. m. muticus_ from the Kansas River at Lawrence, Douglas County, Kansas, were examined (Table 6). The turtles (KU 55296-306, eight adult males and three immature females, ranging in plastral length from 9.0 to 12.5 cm.) were collected in June, 1958, by Mr. Robert R. Patterson. All turtles were caught on hook and line in a period of about four or five hours at dusk. Patterson frequently fished below the bridge at Lawrence and observed that heads of softshells were often seen there about dusk and that the turtles seemed to prefer a rather shallow, quiet-water area of swirls and eddies for feeding. The stomachs, and to a lesser degree, the intestines, were nearly full. Some turtles contained plant fragments, principally elm seeds. The kinds of food in this sample were also identified by Dr. Byers and were mostly insects, the most frequent item being trichopterans; many of the insects eaten undoubtedly fell into the water. The remains of spiders were found in four stomachs and crawfish fragments in five.

Stomachs of two adults of _muticus_ from Lake Texoma, Oklahoma, were opened. The stomach of one (OU 27593) was full of naiads of the burrowing mayfly _Hexagenia_; that of the other female (OU 27594) contained exoskeletal remains of crawfish. The two specimens were drowned in gill nets between the hours of 11 a. m. and 7 p. m., on July 10, 1954; the intact condition of the mayfly naiads indicated recent feeding.

The species of American softshells are mainly carnivorous. The presence of vegetable matter (mentioned in previous paragraphs) in the digestive tracts of many specimens and True's statement (1893:152) that soft-shelled turtles include a variety of vegetable matter in their food indicates omnivorous habits. Duellman and Schwartz (1958:272) stated that _ferox_ is omnivorous and Carr (1952:430) made a similar statement for _spinifer_. The diet seems to be determined by the food supply available, which may vary seasonally or with adverse conditions such as flooding; under normal environmental conditions, however, vegetable matter probably is ingested incidentally to other food. There is no indication of a preference in food habits according to species and subspecies. Most of the food seems to be obtained by active foraging that is triggered primarily by movement of the prey; the sense of smell is probably secondary.

Reproduction

_Size of males at Sexual Maturity_

Elsewhere (1956:121) I have shown that males of _spinifer_ from Lake Texoma, Oklahoma, and scattered localities in Texas and Louisiana are sexually mature when they reach a plastral length of 9.0-10.0 centimeters. Adult males have distinct, convoluted, non-pigmented vasa deferentia and elongate testes, the maximal measurements of which are about 10 by 30 millimeters. Testes of hatchlings are approximately 4.0 by 0.4 millimeters (TU 13698.12, plastral length 3.2 cm., measured with ocular micrometer). I am not aware of seasonal changes in size of the testes.

In reading the discussion that follows, it is well to remember that males having the cloaca extending beyond the posterior edge of the carapace are regarded as sexually mature. As an indication of geographic variation in _spinifer_, I have listed the measurements of the 10 smallest males for only those subspecies of which there are numerous records (Table 7). Corresponding data for _T. muticus muticus_ are also listed for comparison.

TABLE 7. Size at Sexual Maturity of the 10 Smallest Males of T. m. muticus and Selected Subspecies of T. spinifer. The Extremes Precede the Mean (in Parentheses).

========================+======================= SPECIES AND SUBSPECIES | Plastral length (cm.) ------------------------+----------------------- _T. s. spinifer_ | 8.8-10.3 (9.6) _T. s. hartwegi_ | 9.6-10.5 (10.2) _T. s. pallidus_ | 9.1-11.2 (10.5) _T. s. guadalupensis_ | 9.3-10.8 (10.1) _T. s. emoryi_ | 8.2-9.0 (8.8) _T. m. muticus_ | 8.2-9.2 (8.7) ------------------------+-----------------------

The data indicate that the size at which sexual maturity is attained in _emoryi_ (about 8.0-9.0 cm.) is less than in any other subspecies of _T. spinifer_ (about 9.0-10.0 cm.), and, more importantly, corresponds to that of _T. m. muticus_. Although the mean for _T. s. spinifer_ is slightly less than in the remaining subspecies, I doubt that there is any significant difference according to subspecies in the size at which sexual maturity is attained in the subspecies _spinifer_, _hartwegi_, _asper_, _pallidus_ and _guadalupensis_. The corresponding size in _T. m. muticus_ and _T. s. emoryi_ heightens the morphological resemblance between these forms. The only sexually mature male of _T. ater_, which morphologically resembles _emoryi_ and _muticus_, is 9.5 centimeters in plastral length. I do not know the size at which _T. ferox_ attains sexual maturity. The smallest sexually mature individual examined by me was 12.0 centimeters; probably _ferox_ attains sexual maturity at a larger size than _spinifer_ or _muticus_. The relative size of attainment of sexual maturity in _ferox_, _spinifer_, and _muticus_ corresponds to the maximum size of the three species; _ferox_ is the largest species and _muticus_ is the smallest (Table 2).

_Size of Females at Sexual Maturity_

Breckenridge (1955:6) wrote that the development of the mottled pattern "undoubtedly indicates a stage in the attainment of sexual maturity"; I have mentioned (1956:121) that the mottled pattern is apparent on females before sexual maturity is attained. To my knowledge females have no external characters which appear at the time of attainment of sexual maturity.

Sexually mature individuals of _ferox_ have been described in various terms: 31-1/4 pounds (Goff and Goff, 1935:156); six pounds, lengths of carapace 10-1/2 and 13 inches (Hamilton, 1947:209); greatest width of head 3-1/2 inches (Wright and Funkhouser, 1915:120). A 10-1/2 inch carapace presumably represents the smallest turtle and corresponds to a plastron approximately 22.0 centimeters in length. There is no other information available concerning size at sexual maturity in _T. ferox_.

There is little published information concerning the size at sexual maturity in _T. spinifer_. Cahn (1937:193) wrote that _spinifer_ in Illinois "must attain a carapace length of about 24 centimeters [plastral length approximately 18.0 cm.] before the females become sexually mature"; this statement is the basis for Smith's mentioning a length of 9-1/2 inches (1956:162). Evermann and Clark (1920:595) recorded the lengths of carapace of some females (presumably all adult) from Lake Maxinkuckee, Indiana, as 11, 11-3/4, 12-1/2, and 13 inches; the smallest measurement corresponds to a plastral length of approximately 21.0 centimeters.

The data concerning reproduction presented in succeeding paragraphs is based principally upon examinations of turtles in the TU collections; I am indebted to Dr. Fred R. Cagle for permission to dissect these turtles. Females are regarded as sexually mature when they have oviducal eggs or corpora lutea or ovarian follicles exceeding 15 millimeters in diameter. Hatchlings of _spinifer_ have ovaries that measure approximately 6.0 × 0.3 millimeters, and straight oviducts 0.2 millimeters in width (TU 5988, plastral length 3.5 cm. measured with ocular micrometer). In the size at which sexual maturity is attained there seems to be much individual variation as well as geographic variation.

Females of _T. s. emoryi_ from the Río Grande in the Big Bend region of Texas are sexually mature when the plastron is approximately 16.0 centimeters (16.2 cm., KU 51960), and are the smallest adult females of _spinifer_ that I have seen; these females are representative of the population from which the smallest adult males of _spinifer_ are known and which is unique in showing sexual differences in coloration. A female (TU 3697), having a plastral length of 16.0 centimeters, which was obtained in the Río Grande near Eagle Pass, Texas, in mid-July, is immature; the ovaries are compact having the largest follicles 2.5 millimeters in diameter, and the oviduct is wrinkled and convoluted but only six millimeters wide. Of three females of _emoryi_ from the Pecos River, Terrell County, Texas, having plastrons 17.4, 18.3 and 18.8 centimeters in length and obtained on June 11, the largest and smallest are immature, and internally resemble TU 3697. TU 14453.2 (18.3 cm.) is sexually mature having large corpora lutea and enlarged ovarian follicles. KU 53754, from the Río Salado in central Coahuila, México, having corpora lutea and a plastral length of 20.3 centimeters, is sexually mature.

Females of _T. s. guadalupensis_, measuring 14.5, 15.7, 16.3, 16.5, 16.8, 17.0, 19.0, and 20.0 centimeters in plastral length and obtained from June to September, are immature. The female measuring 19.0 centimeters indicates the approach of sexual maturity in having swollen and convoluted oviducts seven to ten millimeters in width, but compact ovaries having the largest follicles 4.0 millimeters. The other _guadalupensis_ whose measurements are given above have oviducts that do not exceed four millimeters in width, and ovarian follicles that do not exceed two millimeters in diameter. TU 10187, obtained in July, plastral length 19.5 centimeters, is sexually mature having corpora lutea and enlarged follicles. Two other _guadalupensis_, 21.5 and 22.0 centimeters (Pl. 12, top), having ovaries with enlarged ovarian follicles (the largest in one, only 11 mm.) are considered sexually mature.

Concerning the subspecies _pallidus_, females (all collected in June or July) measuring 15.7, 16.3, 17.3, 17.5, 18.7, 19.5, 20.8 and 21.3 centimeters in plastral length are immature having solid, compact ovaries with the largest follicles not exceeding two millimeters in diameter; oviducts are straight not exceeding three millimeters in greatest width, except those turtles measuring 17.3 and 21.3 centimeters in which the oviducts are swollen and convoluted and, respectively, five and eight millimeters in greatest width. The smallest sexually mature _pallidus_ is 19.8 centimeters in length; recorded lengths of other adult females are 23.5, 26.8 and 30.5 centimeters.

Of especial interest are three large female _pallidus_, measuring 24.8, 27.5, and 28.0 centimeters, which appear to be immature; two of these (TU 13303-04) are from the Sabine River, collected in July, and the other specimen is without data (presumably from the Sabine River). The oviducts are large, swollen and convoluted, resembling those in sexually mature individuals. The ovaries, however, are relatively solid and compact having approximate measurements of 125 × 6 millimeters (TU 13303) and 85 × 10 millimeters (TU 13304), and follicles not exceeding five millimeters in diameter.

Females of _spinifer_ from the lower Mississippi Valley of Louisiana having plastral lengths of 15.0, 15.5, 16.7, 17.5, 18.0, 19.5, 20.0, 20.4, and 20.8 centimeters are considered immature; the ovaries are compact and solid having follicles not exceeding three millimeters in diameter, and the oviducts, swollen and convoluted in the larger individuals, do not exceed six millimeters in width. The ovaries of the specimen 19.5 centimeters in length mentioned immediately above had been removed prior to my examination; the oviducts, however, were relatively straight and only five millimeters in width. Three females 23.0, 25.5, and 25.8 centimeters in length are sexually mature. TU 5518, measuring 21.5 centimeters in length and obtained in June, indicates the onset of sexual maturity in having large convoluted oviducts, but the ovaries are solid, compact, measuring 85 × 13 millimeters, and the largest follicles are only 4.5 millimeters. A larger turtle (TU 13080), 24.5 centimeters, obtained in July, has juvenal ovaries (largest follicles five mm.); the oviducts are enlarged and convoluted as in adult females.

Of two _T. s. asper_ collected from the Escambia River in June and July, one 18.0 centimeters in plastral length is immature, whereas the other, 27.0 centimeters long, is adult. A female _T. s. hartwegi_, measuring 20.7 centimeters, is adult having enlarged follicles and corpora lutea (TTC 719, Pl. 36, bottom).

In summary, females of all subspecies of _spinifer_, except some _emoryi_, may be sexually mature when the plastron is 18.0 to 20.0 centimeters in length; probably all physiologically normal females are adult when 22.0 centimeters long. In general, females are sexually mature at a plastral length of approximately 20.0 centimeters, a measurement that corresponds to a length of carapace of approximately 28.0 centimeters or about 11 inches. Females representative of that population of _emoryi_ inhabiting the Río Conchos and the Río Grande in the Big Bend region of Texas are adult when the plastron is approximately 16.0 centimeters in length, and are thus the smallest sexually mature females of the species _spinifer_. Oviducts are large (at least eight mm. in width, undistended), swollen and convoluted prior to the first ovulation.

Of interest are the large females (for example, TU 13303, plastral length 28.0 cm.) that seemingly have immature, relatively small, ovaries (the oviducts are large and convoluted as in adult females). Possibly such ovaries represent a regression and are in senile turtles, but I am inclined to believe that the development of these ovaries has been arrested probably owing to hormonal unbalance, and that they have never been functional.

The size of adult females of _T. ater_ is unknown but probably approximates that of _T. spinifer_ or is slightly less. Females of _ater_ 15.5 and 17.2 centimeters in length are immature; the largest female, the holotype, is 18.3 centimeters in length, and was not dissected.

Females of _T. muticus_ are sexually mature when smaller than _T. spinifer_. Two turtles, 13.8 and 14.0 centimeters in length, have large convoluted oviducts about 10 millimeters in width and ovarian follicles nine to twelve millimeters in diameter, and seem to be near sexual maturity. The smallest sexually mature female (subspecies _muticus_) is TU 14436, measuring 14.4 centimeters in plastral length and having oviducal eggs. Recorded lengths of other adult females are 16.3, 16.5, 17.2 (subspecies _muticus_), and 18.0 centimeters (subspecies _calvatus_). Two females having plastral lengths of 17.5 (subspecies _muticus_) and 16.0 centimeters (subspecies _calvatus_) seem sexually immature. These turtles collected in April and May have ovarian follicles not exceeding three millimeters in diameter.

_Sexual Activity_

Observations by Mitsukuri (1905:263), Conant (1951:160) and Legler (1955:98), constitute the extent of our knowledge concerning courtship and copulation. Legler observed a male _spinifer_ and a female _muticus_ in captivity; the male was the aggressor, following at the rear or above the female, and at times nipping at the anterior part of her carapace. During these movements, the posterior edge of the female's carapace was turned up slightly whereas that of the male was turned down; the turtles frequently surfaced to breathe. Occasionally the female followed the male. On the bottom the male crawled onto the female's carapace from the rear, remaining in a somewhat posterior position as described by Conant (_loc. cit._), and seemingly not clasping the female with his feet. Copulation probably occurs in this position; Mitsukuri (_loc. cit._) mentioned that copulation in _Trionyx sinensis_ occurs at the surface of the water. The male remains in the coital position for approximately 15 seconds and then slowly drifts to one side and swims away. Legler observed five coital unions in one-half hour, each preceded by courting movements.

Legler's observations indicate that the courtship patterns of _muticus_ and _spinifer_ are similar, and that interspecific matings are possible. I have not noted any hybrid.

Risley (1933:689) mentioned differential movements of the sexes of _Sternothaerus odoratus_ in conjunction with the breeding cycle. Such movements are revealed by trapping procedures that yield deviations from the expected 1:1 sex ratio. That differential sexual movements probably occur in _Trionyx_ is indicated by my trapping 17 males in a group of 19 _spinifer_ in hoop-nets in Lake Texoma in the period June 14-July 12, 1954. On June 24-26, 1959, a field party from the University of Kansas collected 15 softshells in hoop-nets at the mouth of the Río San Pedro, near Meoquí, Chihuahua; all turtles were males. On June 17-18, 1959, the same expedition trapped 11 males in a group of 13 turtles in the Río Conchos, near Ojinaga, Chihuahua. Earlier, June 12-14, 1959, 39 softshells were trapped in the Río Grande near Lajitas, Brewster County, Texas. Of these turtles, however, 19 were adult males and 20 were females; eight females were adult (sexually mature) all having oviducal eggs (Fig. 23). One of the two females from Ojinaga, KU 51174, is sexually mature (plastral length, 16.5 cm.) having oviducal eggs; the other is immature (plastral length, 8.0 cm.). The only softshell taken on June 21, 1959, 8 mi. N and 16 mi. W Ojinaga, KU 51173 (plastral length, 16.3 cm.) is a female having oviducal eggs. The two females from Lake Texoma are immature (plastral lengths, 9.8 and 12.4 cm.).

The results of trapping may indicate that females frequent shallow water for a short time before the period of deposition of eggs, but disperse to deep water after such periods or between them. The movements of immature females probably approximate those of adult males; the absence of immature females in the Meoquí series, and near absence (only one) in the Ojinaga series perhaps is due to fortuitous collecting methods or to slightly different diurnal movements between adult males and immature females. Females approaching sexual maturity and those sexually mature but not having oviducal eggs ready for deposition possibly remain relatively sedentary in deep water; such females possibly represent those absent in the 13.0-15.9 size group (Fig. 23). Certainly, factors other than those pertaining to egg deposition may cause mature egg-laden females to live in shallow water, or explain the deviations from the expected 1:1 ratio.

One of the immature softshells (KU 51979, plastral length, 9.7 cm.) of the series from Lajitas is considered to be a female. It combines characteristics of both sexes. It resembles a male in having a carapace gritty to the touch, in having prominent white dots posteriorly and in not having a faint mottled and blotched pattern as do females of the same size. The postocular and postlabial markings are mostly yellow (female), but a small patch of the postocular stripe near the junction with the pale ventral coloration laterally is tinted with orange (male); the morphological characters and secondary sexual difference in coloration of this series of softshells has been mentioned on page 512. The tail is short and pyramidal resembling that of a female. Internally, there are a pair of ovaries and oviducts; KU 51979 is functionally a female. An over-production of androgens probably is responsible for the external masculine characteristics (orange color, gritty carapace and absence of mottling on carapace).

_Deposition of Eggs_

Concerning _T. ferox_, Wright and Funkhouser (1915:122-23) wrote that deposition of eggs occurred in June and July in the Okefinokee Swamp on the sandy parts of the islands or in sandy fields in places exposed to the direct rays of the sun. The same authors recorded a gravid female taken on June 22 (_op. cit._:120), and a nest with eggs on June 26. Harper (1926:415) reported egg-laying in June in the Okefinokee Swamp. Goff and Goff (1935:156) found a female in search of a nesting site crawling toward a cleared area within a hammock at 11 a. m. on May 19, about 25 yards from the western shore of Lake Griffin, Florida. Carr (1940:107) stated that eggs in Florida "are laid from March to July 10. One individual laid her eggs on a block of ice which we had buried in the sand." Hamilton (1947:209) observed deposition of eggs near Fort Myers, Florida, in "a sandy roadbed slightly above the cypress swamp and ditch levels on either side of the road." ... either in ... "the ruts formed by cars or the slope of the roadbed"; dates of deposition of eggs recorded are March 30 at 11 a. m. in bright sun, and March 31 (from context, the date given as March 21 is considered an error) at 5 p. m. following a heavy rain. The daily temperatures at the time of Hamilton's observations "averaged 85° F., the first really warm spell of the season."

Eigenmann (1896:262) reported egg-laying of _spinifer_ in sand and gravel in June and July at Turkey Lake (= Lake Wawasee), Indiana. A turtle was seen digging a nest on June 26, and fresh nests of eggs were found on June 27 and July 9. Hedrick and Holmes (1956:126) wrote that a clutch of eggs of _spinifer_ in Minnesota was found about ten inches deep in sand about one foot from the river; a steep gravel bank was also cited as a favorite nesting site. Surface (1908:123) stated that eggs of _spinifer_ in Pennsylvania are laid in May, and the young hatch in August. Gehlbach and Collette (1959:142) found eggs of _spinifer_ on June 19 on a sand bank 15 feet from the edge of the Platte River in Nebraska. Breckenridge (1944:187) wrote that _spinifer_ in Minnesota nests on sandy beaches from June 14 to July 6. Cahn (1937:193) stated that deposition of eggs in Illinois occurs in "June or early July: earlier in the southern part of the state, later in the northern portion." Force (1930:38) mentioned a gravid female from Oklahoma obtained on May 20. Evermann and Clark (1920:593) were of the opinion that _spinifer_ began laying about mid-June and continued until perhaps late July at Lake Maxinkuckee, Indiana; a female opened on June 14 had oviducal eggs, and the first nest was found on June 18. Nests were usually at the edge of an abrupt ascent in sand; one nest was found in black, mucky soil (_op. cit._:595). Newman (1906:128) wrote that _spinifer_ in the same lake nests later than the other species of turtles, as a rule not earlier than the middle of June (but as early as June 10, _op. cit._:132), and rarely later than the middle of July; he observed deposition of eggs on June 22. Sites of deposition of eggs were mostly in soft sand not more than six feet from water; other sites found by Newman (_op. cit._:132-33) were a sandy, abandoned road bed separated from the shore by a strip of tall grass, a rock pile (the eggs being dropped into crevices and sand packed around them), among roots of a tree (the eggs being deposited between the roots and under them in a very irregular fashion), and in clay "so hard packed that one could scarcely break it with the fingers." Natural nest sites in hard clay and a rock pile seem incongruous with nesting habits of softshells. I note that Newman's study was not begun until 1902 (_op. cit._:127), and it was that year that the water level of the lake was high, flooding the surrounding lowlands (Evermann and Clark, 1920:49-53). Perhaps some of the nests found by Newman were old and not natural because of conditions resulting from the receding water level.

Newman (_op. cit._:134-35) mentioned that in small sandy areas nests were frequently in contact and overlapped; he found one nest containing nine small eggs contiguous with 23 large eggs. Breckenridge (1944:187) reported a nest of 56 eggs of two slightly differing sizes, and probably from two females. Evermann and Clark (1920:594) discovered "probably 10 or 12 nests in a distance of a few yards" and mentioned one nest containing 25 eggs "that evidently belonged to two different sets ... In the bottom were 10 eggs that looked old ... and ... separated from them by sand, were 15 other eggs."

Nesting sites of _muticus_ were mentioned by Muller (1921:181) on one of several small islands having "gently sloping sand and mud shores, and interior areas of open sand and densely growing willows" in the Mississippi River, near Fairport, Iowa. The same author wrote that the egg-laying season is from late June to early July, and that the female selected a place 10 to 60 feet inland "with an unobstructed view of the open water." Farther north on the Mississippi River near Dubuque, Iowa, Goldsmith (1945:447) found that _muticus_ preferred "clean, somewhat level sandbars and sandy shores free from trash, weeds ... and exposed to open view." The same species, however, may "make unsatisfactory nests ... in any place they can find sand, even in the weeds and bushes ... when the river is high, covering the sandy plots ..." Sometimes nests, which were "seldom nearer than six feet or more than twenty-five feet from water ...," were submerged by a rise in water level. In Missouri, Hurter (1911:251) found that individuals of _muticus_ came "... out on the sandbars in the Mississippi River to deposit their eggs ... At the end of May up to the middle of June ..." Cahn (1937:182) wrote that the nesting season of _muticus_ is early July near Meredosia, Illinois. Anderson (1958:212, Fig. 1) found nests of _muticus_ along the Pearl River in Louisiana on an open sandbar (not in gravel, fine sand or silt), whereas nests of _Graptemys_ were confined to the landward margin of the sandbar.

The onset and length of the breeding season seems to be geared to the climatic conditions under which the species occurs, and, as would be expected, begins earlier and lasts longer in southern latitudes than in northern latitudes. The period of deposition of eggs in _T. ferox_ (Florida) is from late March to mid-July, whereas that of northern populations of _spinifer_ and _muticus_ (southern Great Lakes region) is usually from mid-June to mid-July.

Seemingly there is little difference between species in preference of nesting sites; a sandy substrate is probably preferred. Gravid females of _ferox_ and _spinifer_ may wander overland some distance and select places where the view of the water is obstructed by vegetation; both species may wander little and nest in full view of the water. Concerning _muticus_, it is of interest that of the many nests discovered by Anderson (_loc. cit._) on an open sandbar, all were those of _muticus_ and none was a nest of _spinifer_. The nests of _muticus_ mentioned by Muller (_loc. cit._) and Goldsmith (_loc. cit._) were on open sandbars. On June 4, 1953, six clutches of eggs were found on an open sandbar of the Escambia River, Florida; all hatchlings from those eggs that were successfully incubated were _muticus_. On June 1, 1954, three nests were found on an open sandbar of the same river (Pl. 50); the temperature within the nests at 6:30 a. m. was approximately 25° C. Two nests were dug in a sand substrate on the level portion of the bar (Pl. 51, Fig. 1). The third clutch of eggs was deposited in a sand-gravel substrate at the brim of the incline from the shore (approximately 30 degrees and about five feet above the water); the eggs of this clutch were arranged rather symmetrically (Pl. 51, Fig. 2). Unfortunately, most of the eggs from these three clutches failed to hatch. Although the data are far from conclusive, I have the impression that _muticus_ limits its sites of egg deposition to the open regions of sand bars and does not lay inland where it must traverse vegetated areas unless preferred nesting sites are submerged or otherwise unsatisfactory. Females of _spinifer_ may utilize open sandbars for deposition of eggs but not areas where _muticus_ occurs. In areas where both _muticus_ and _spinifer_ occur, the latter probably lays farther inland or on the landward margins of sandbars.

Excavation of nests has been observed in _ferox_ (Hamilton, 1947:209), _muticus_ (Muller, 1921:181-82; Goldsmith, 1945:448), and _spinifer_ (Newman, 1906:132-33; Cahn, 1937:191-92; Breckenridge, 1960:284). Turtles leaving the water are cautious, usually stopping and extending the neck to its greatest length, holding the head high, and sometimes returning to the water for a short time. Depending on the condition of the substrate and wariness of the female, nest construction may begin immediately, or several holes may be dug and then abandoned. The excavation on level ground or a slight incline is made by means of the hind feet (Muller mentions digging with the forefeet; I agree with Pope, 1949:321, and Conant, 1951:264, who consider Muller in error); the forefeet are firmly planted and not moved during the excavation, deposition of eggs or the filling of the nest cavity. The hind feet are used alternately; cloacal water may be used to facilitate digging or to provide a suitable substrate for the eggs. Cahn mentioned that some sand may be flung four or five feet, and that during the digging the head is held high. Breckenridge (_loc. cit._) reported that sand was thrown a distance of ten feet. The nest may be completed in 16 minutes (Cahn, _loc. cit._) or less than 40 minutes (Newman, _loc. cit._). Breckenridge recorded 17 eggs laid in six minutes, Cahn recorded 12 eggs laid in eight minutes, and Hamilton recorded four eggs laid in three minutes. The hind feet are used to arrange the eggs and are used alternately to fill the nest cavity; sometimes a little sand is scraped in before all the eggs are deposited. Muller recorded the nest cavity as five inches in diameter and ten inches deep, the finished nest appearing "as a small crater ... about a foot in diameter, or where the surface is covered with pebbles, as a circular area of clear sand." Goldsmith reported that the nest cavity was six to nine inches in depth, and that after deposition and filling with sand "By certain twisting movements with all four legs, she drags the plastron around over the sand, making a perfect camouflage." Newman found the nest flask-shaped having a depth of about six inches, and diameters of about three inches at the bottom and one and one-half inches in the neck. Hamilton described a flask-shaped nest, the entrance of which would "barely permit the passage of an egg ... the bottom, at a depth of five inches, being about the width of a quart milk bottle." Cahn related that the "hole descended at an angle of about 60°," and the eggs thus rolled down an inclined plane.

Possibly the nests of _ferox_ and _spinifer_ differ from those of _muticus_ in being flask-shaped. A nest of _spinifer_ was reported by Gehlbach and Collette (_loc. cit._) as having a neck three inches across, a depth of six inches and a width of five inches at the bottom. The nests of _muticus_ that I discovered on the Escambia River were not flask-shaped; the eggs were five to seven inches below the surface. Evermann and Clark (1920:594) reported eggs of _spinifer_ "generally at a depth of four to ten inches," and Breckenridge (_loc. cit._) found the topmost eggs about five inches below the surface. There may be behavioral differences between _ferox_ and _spinifer_ and _muticus_. Hamilton (_loc. cit._) mentioned that _ferox_ proceeded with its reproductive duties even when he stood only a few yards away. Muller (_op. cit._:181) found that _muticus_ would run to the water if disturbed, without completing deposition of eggs; the same behavior was described by Cahn (_op. cit._:191) for _spinifer_. Newman (1906:133) wrote that _spinifer_ will abandon nesting activities if surprised before egg deposition begins, but will wait to cover the eggs if interrupted while laying eggs. Goldsmith (1945:448) found that an observer did not disturb females of _muticus_ when they were laying eggs (females "could be approached and even touched"), but that, in the presence of an observer, they would scurry toward the water without covering the eggs and would not return to cover them. Turtles frightened in the process of the construction of the nests would not return to complete the original nest. Harper (1926:415) wrote that _ferox_, after completing nesting activities, will crawl a few feet from the nest and scuffle up the surface, presumably to decoy predators that might otherwise destroy the eggs; this observation has not been corroborated by other authors. Harper (_op. cit._:416) recorded the observation of Allen Chesser, who says that females, after egg deposition, often "... bury themselves, before they go ter the water, an' stay there ten er twelve hours."

_Reproductive Potential_

Estimates of reproductive potentials are subject to variation of one kind or another. Counts of oviducal eggs or those in nests may be misleading, as in some individuals one or more eggs may have been deposited previously. Mitsukuri (1905:263), Newman (1906:135), Muller (1921:182), and Cahn (1937:183) have mentioned that the number of eggs per clutch corresponds to the size of the female. Females of northern populations may have larger clutches than females of the same size from southern populations.

TABLE 8. Records in the Literature Pertaining to Number and Size of Eggs of Three American Species of Trionyx.

===========+=====================+===================+======================= | Number of eggs per | | | clutch; oviducal | Size of eggs; | Authority SPECIES | (o), nest (n); | ave. = average | and remarks | ave. = average | | -----------+---------------------+-------------------+----------------------- _ferox_ | | 24 mm. | Agassiz (1857, pl. 7, | | | fig. 20); nat. size. | | | | 22 (n) | ave. 31 mm. | Wright and Funkhouser | | | (1915:120) | | | | some (o) | 32 mm. | " | | | | 20 (o) | ave. 25 mm., and | Goff and Goff | | 12 gms. | (1935:156) | | | | 17 (o) | ave. 27 mm. | Hamilton (1947:209) | | | | 21 (o) | | " | | | | 7 (o) | | " (egg | | | deposition probably | | | interrupted) -----------+---------------------+-------------------+----------------------- _spinifer_ | | 29 mm., 26.5 mm. | Agassiz (1857, pl. 7, | | | figs. 20 and 23, | | | respectively); nat. | | | size. | | | | 9, 12, 17, 18, 27 | | Eigenmann (1896:263); | and 32 | | northern Indiana | | | | 9 to 24, ave. 18 | | Newman (1906:135); | | | northern Indiana | | | | about 30 (n), 4 | 1.09 × 1 inch | Evermann and Clark | (n), 3 (n) | | (1920:593-94); | | | northern Indiana | | | | 21 (n and o) | (o) and some (n) | " | | .93 × .93 inches; | | | rest of (n) 1.07 | | | × 1.07 inches | | | | | 32 (o) | ave. 1-1/4 inches | Force (1930:38); | | | Oklahoma | | | | 9, 12, 13, 15, 17, | ave. 28.3 mm. | Cahn (1937:193); | 19, 19, 21, 22, 23, | (217 eggs) | Illinois | and 25; ave. 18 | | | | | | 12 (o), 26 (o), 24 | 22.0 to 28.5 mm. | Breckenridge | (n), and 30 (n) | | (1944:187); Minnesota | | | | 21 (o) | 24 to 27.8 (ave. | Conant (1951:160); | | 25.6 mm.) × | Michigan | | 25.8 to 29 (ave. | | | 27 mm.) | | | | | 22 (n), 22 or | | Hedrick and Holmes | 23 (n) | | (1956:126); Minnesota | | | | 25 (n) | ave. 24 × 25.2 | Gehlbach and Collette | | mm. | (1959:142); Nebraska | | | | 17 (n) | | Breckenridge | | | (1960:284); Minnesota -----------+---------------------+-------------------+----------------------- _muticus_ | | about 22 mm. | Agassiz (1857, pl. 7, | | | fig. 21); nat. size. | | | | 21 | about 20 mm. | Hurter (1911:249); | | | Missouri | | | | 4, 12, 13, 16, 21, | ave. 2.3 cm. and | Muller (1921:182); | 22, 26, and 33, all | 7 gms. | Iowa | (n); ave. 22 | | | | | | 18 to 22, maximum | ave. 22.6 mm. | Cahn (1937:183); | 31 | (116 eggs) | Illinois | | | | 93 from 5 nests, | variable--largest | Goldsmith (1945:449); | ave. 18.6; 10, 10, | _ca._ 1-3/8 | Iowa | 16, 17, 17, 19, 21, | inches, smallest | | 21, 22, 22, 31, all | less than one | | (n), ave. 18.7 | inch. | -----------+---------------------+-------------------+-----------------------

Additional records of size of clutch are provided by data from dissected females (Table 9). All females were collected from May through September from localities south of latitude 36.5°. The number of eggs includes those in both oviducts, and the number of ovarian follicles those in both ovaries. The number and range in size of only the largest group of follicles is listed; in some instances the size of follicles formed a graded series, and the designation of a group was arbitrary.

TABLE 9. Length, Number of Oviducal Eggs, and Condition of Ovaries in Adult Females of T. spinifer and T. muticus.

===========+========================+=========+====================== | | | Ovarian follicles | | | (total) SPECIES | Size of female | Eggs +---------+------------ | (plastral length, cm.) | (total) | | | | | Number | Size (mm.) -----------+------------------------+---------+---------+------------ _muticus_ | 14.4 | 6 | 14 | 15-18 | 16.3 | 9 | 4 | 15-17 | 16.5 | | 3 | 16 | 16.5 | 3 | 4 | 14-18 | 17.2 | | 13 | 14-21 | 27.0 | | 25 | 18-21 -----------+------------------------+---------+---------+------------ _spinifer_ | 16.2 | 7 | 4 | 16-20 | 16.2 | 7 | 5 | 18-20 | 16.2 | 7 | 1 | 18 | 16.3 | 6 | 5 | 16-18 | 16.3 | 4 | 5 | 15-19 | 16.8 | 6 | 1 | 18 | 17.3 | 3 | 2 | 17 | 18.3 | | 13 | 19-20 | 19.5 | | 2 | 17 | 19.8 | | 4 | 20 | 20.7 | | 11 | 15-18 | 21.5 | | 6 | 8-11 | 22.0 | | 13 | 11-14 | 23.5 | 8 | 12 | 20-24 | 25.5 | 11 | several | 18-22 | 25.8 | 13 | ? | 18-21 | 26.8 | 10 | 5 | 18-20 | 30.5 | 13 | 5 | 20-21 | | 16 | 16 | 16-21 | | 11 | 19 | 15-20 | | 17 | 23 | 18-22 | | 17 | 22 | 14-20 | | 8 | 15 | 18-22 -----------+------------------------+---------+---------+------------

Published data (Table 8) indicate that the average number of eggs per clutch for the three American species is about 20, although the number of eggs may exceed 30 in _spinifer_ and _muticus_. Except for those of _ferox_, most of these records are based on observations in northern latitudes (approximately 40°). My examination of females from southern latitudes (below 36.5°) reveals no oviducal egg count greater than 17 and an average number of eggs per clutch of 9.6 per _spinifer_ (Table 9); that of _muticus_ is 7.3, as based on data given in Table 9 as well as on egg-nest counts of 15, 6, 6, 6, 6, 5, 9, 8, and 8. Ovarian follicles larger than 15 millimeters in diameter are arbitrarily considered to comprise the next clutch that will be deposited in the current season. Follicles of this size possibly are retained until the following year or some may undergo regression; some of the included follicles may not be representative of the succeeding egg complement. The average number of follicles of the most enlarged groups is 9.0 for _spinifer_ and 10.5 for _muticus_. Females in northern latitudes probably have a greater reproductive potential than those in southern latitudes if it is assumed that there is only one laying per season for an individual; the maximum number of eggs laid at any one time probably does not exceed 35. There is also an indication that larger females deposit more eggs than smaller females (Table 9). Muller (1921:184) mentioned two double eggs (each having two yolks) in the complement of 33, indicating an abnormally large number and excessive crowding of eggs in the oviducts. Simkins (1925:188) also mentioned some eggs of a clutch (form and locality unknown) that were five or six millimeters larger (about 31-32 mm.) than the rest, and which "invariably bore twins." The largest number of eggs in a single nest mentioned by Simkins is 22. If the presence of double-yolked eggs is indicative of crowding of eggs in the oviducts, the egg complements of 22 and 33 indicate the approximate maximal number of eggs per clutch. In the species _spinifer_, the average size of sexually mature females is slightly smaller at some places in the south than in the north. Therefore, smaller clutches are to be expected in the south.

Many of the females collected in June or July contained corpora lutea four to eight millimeters in diameter in addition to enlarged ovarian follicles. Presumably the corpora lutea indicate clutches deposited earlier in the current season, and the enlarged follicles represent clutches to be deposited in the current season. One female of _muticus_ (OU 27593) obtained on July 10, contains oviducal eggs, ovarian follicles 15-17 millimeters in diameter, and corpora lutea of different sizes that exceed the number of oviducal eggs; possibly this female was capable of laying three clutches each season. Corpora lutea, representing ovulation points of eggs in the oviducts, are approximately eight millimeters in diameter. In order to establish definitely the reproductive potentials of any species of turtle, it is desirable to know the approximate size of ovarian follicles that are retained by sexually inactive females, and the rate of regression of the corpora lutea. The data suggest that, in southern populations at least, two and possibly three clutches of eggs are deposited in the annual breeding season. Mitsukuri (_in_ Cagle, 1950:38) found that _T. sinensis_ deposited four groups of eggs each season.

It is suggested that the seasonal reproductive potential of northern populations (averaging about 20 eggs per clutch, and probably one clutch per season) is less than that for southern populations (averaging about 10 eggs per clutch, but three clutches per season). But owing to variation, there may be no great discrepancy between the actual potentials of northern and southern populations.

_Eggs_

The eggs of _Trionyx_ are white and spherical having a brittle shell. Some eggs are occasionally abnormal in shape and size; overcrowding of eggs in the oviducts may result in small, irregular-shaped eggs, or large double-yolked eggs. Presumably enlargement of the eggs occurs in the oviducts and within a short period after deposition prior to complete hardening of the brittle shell; therefore some eggs in the oviducts are smaller than those in nests.

The data concerning _ferox_ (Table 8) suggest that the maximum size of eggs is 31 to 32 millimeters, whereas oviducal eggs are slightly smaller, about 25 to 27 millimeters. Eggs of _spinifer_ from northern latitudes (most from approximately 40°, Table 8) also vary in size, oviducal eggs being as small as 22 millimeters in diameter and the maximal size about 29 millimeters. Average extreme measurements (in mm.) of oviducal eggs (number of eggs in parentheses) from females taken in latitudes of 33 degrees or less are: 25 × 29 (11), 29 × 30 (11), 28 × 30 (13), 28 × 30 (10), 29 × 30 (5), 29 × 29 (8), 25 × 26 (17), 29 × 30 (5), and 28 × 29 (8). The average size of these eggs is slightly larger than the oviducal eggs of which measurements are given in Table 8, and suggest larger eggs from more southern latitudes. Eggs of _muticus_ are smaller than those of _spinifer_ (Cahn, 1937:183) or _ferox_; the average size of eggs from nests found in Iowa and Illinois is 22 to 23 millimeters (Table 8). Nine oviducal eggs from a female obtained in Lake Texoma, Oklahoma, averaged 22 × 23 millimeters. The largest eggs of _muticus_ are from the southernmost locality; eight eggs from a nest found along the Escambia River, Florida, averaged 26 × 27 millimeters.

In general, the data suggest that at each laying slightly smaller eggs but larger numbers are laid by females in northern latitudes, whereas larger but fewer eggs are laid by females from farther south.

_Incubation and Hatching_

Length of the incubation period seems to depend upon conditions of heat and moisture, and, in general, to be geared to the prevailing climatic conditions. Goff and Goff (1935:156) artificially incubated some eggs of _ferox_ at temperatures varying from 82.3 to 89.2° F., and found that the incubation period was 64 days. Muller (1921:184) wrote that the period of incubation of eggs of _muticus_ (natural nests at temperatures about 90°., _op. cit._:182, and artificial nests) in Iowa is from 70 to 75 days. Breckenridge (1944:187) stated that _spinifer_ makes nests in Minnesota from June 14 to July 6, and cited reports that indicate hatching in September. Hedrick and Holmes (1956:126) discovered a nest of eggs in Minnesota on September 5; the eggs were artificially incubated and some hatched on October 29. Eigenmann (1896:263) found eggs as late as September in northern Indiana that "contained young which would have been ready to hatch about a month later." Cahn (1937:193) wrote that _spinifer_ in Illinois lays in June or early July and that "young-of-the-year are taken in late August and September." Some recently deposited eggs of _muticus_ (as indicated by fresh turtle tracks, Pl. 50, Fig. 2) that I obtained on June 1 were artificially incubated and hatched on August 4, indicating an approximate incubation period of 65 days. Dr. Paul K. Anderson in the course of field work on the Pearl River, Louisiana (1958:211), found that eggs collected on June 13 from a nest excavated three to five days before, hatched on August 15, indicating an incubation period of approximately 67 days. Eggs collected on May 17 to 25 (three clutches) hatched on August 4 to 6, indicating an incubation period of approximately 77 days. In any latitude the incubation period probably is at least 60 days. Eigenmann (_loc. cit._), however, mentioned empty nests that were found in July; this indicates early hatching or more probably the action of predators.

In northern latitudes eggs or young turtles may over-winter in the nest if deposition is late in the season. In northern Indiana Evermann and Clark (1920:595) found a nest on November 16 that contained "well-formed young" and believed that the turtles would have wintered in the nest. Conant (1951:160) was of the opinion that most eggs probably hatch in early fall, but that some do not hatch until spring.

The hatching of eggs of _muticus_ has been described by Muller (1921:183). According to him, the forelimbs first emerge through the shell and enlarge the opening. There is an "egg tooth below the flexible proboscis" but "it does not seem to be used in escape from the eggs, and is dropped a week after hatching." Hatchlings burrow almost straight upward through the sand leaving the egg shell below the surface and a hole in the sand about an inch in diameter. Muller found that young turtles emerge from the nests in the night or early morning and always go downhill probably influenced in their movements by the open sky and sloping beach. Anderson (1958:212-15) found that hatchlings of _muticus_ leave nests within the first three hours after sunset and travel a direct route to the water. He discovered that hatchlings are active on the surface of the sand at night and generally show a positive reaction to light (moonlight, flashlight), whereas, in daytime, there is a negative reaction to bright sunlight (causing the turtles to bury themselves in sand). Anderson believed that the positive response to light at night is not correlated with the water-approach behavior of hatchlings, but that movements to water are possibly influenced by a negative reaction to dark masses of environment (such as shadows formed by landward forests).

_Age and Growth_

Goff and Goff (1935:156) found that hatchlings of _ferox_ average 8.82 grams (extremes, 8.50 to 9.25); one of these, UMMZ 76755, is illustrated in Plate 31. Muller (1921:184) recorded measurements of five hatchlings of _muticus_; the average measurements (in cm., extremes in parentheses) were: length of carapace, 3.54 (3.43 to 3.67); width of carapace, 3.20 (3.10 to 3.25); length of plastron, 2.54 (2.47 to 2.60). I recorded measurements of 32 hatchlings (three clutches combined) of _muticus_ on August 16; the turtles hatched on August 4 to 6 from eggs collected along the Pearl River, Louisiana. The average measurements (in mm., extremes in parentheses) of the 32 turtles were: length of carapace, 41.3 (34.0 to 45.0); width of carapace, 38.6 (31.0 to 40.0); length of plastron, 30.1 (25.0 to 32.0). These turtles have circular umbilical scars averaging approximately two millimeters in diameter. The smallest hatchling that I have seen measures 21.0 millimeters in plastral length (_T. m. muticus_, INHS 3458). There are no data to indicate a difference in size of hatchlings among the American species of soft-shelled turtles. The average plastral length of most hatchlings probably is 28.0 to 30.0 millimeters.

Owing to the lack of a horny epidermal covering of the carapace and plastron, soft-shelled turtles are not so well suited to studies of age and growth as are the "hard-shelled" species, which have visible impressions of growth annuli on the epidermal scutes. Mattox (1936:255) found annular rings in the long bones of specimens of _Chrysemys_ and suggested that it is tenable to correlate the number of rings with the age of the turtle.

Mitsukuri (1905:265) reported that in hatchlings of _Trionyx sinensis_ the length of the carapace averages 2.7 centimeters (hatchlings of _sinensis_ seem to average smaller than any American species), and that the average length of carapace (cm.) at the end of the first year is 4.5, second year 10.5, third year 12.5, fourth year 16.0, and end of fifth year 17.5; he stated also that females of _sinensis_ are sexually mature in their sixth year. Breckenridge (1955:7-9) computed a growth curve based on 11 recaptures of females of _spinifer_ in Minnesota; his data on rate of growth for the first five years do not differ appreciably from those of Mitsukuri. As most females of _spinifer_ are sexually mature when the carapace is about 11 inches long, the age at sexual maturity is approximately 12 years according to Breckenridge (_op. cit._:8, Fig. 4). The discrepancy in age of females at the size of attainment of sexual maturity (Mitsukuri--six years; Breckenridge--12 years) is, in part, rectified by the fact that _Trionyx sinensis_ probably is a smaller species. Also, Breckenridge's computation of the growth curve is based on continuously decreasing increments of growth and seemingly eliminates consideration of the probable marked decrease in rate of growth that occurs when sexual maturity is attained--a phenomenon noted in other species of turtles. I think that increments of growth of immature turtles are, on the average, larger than those of sexually mature turtles. Judging from these criteria, the age of a female of _spinifer_ at sexual maturity is less than 12 years, and turtles having carapaces 17 to 18 inches in length (maximal size for _spinifer_) would be older than 53 years (_op. cit._:9). Occasional individuals, however, may greatly exceed the usual growth rate in which event large adults may be younger than 50 years.

Females of _muticus_ are sexually mature when the plastron is 14.0 to 16.0 centimeters long, which corresponds to a carapace 19.6 to 22.4 centimeters (about 7-3/4 to 8-3/4 inches) long (average CL/PL approximately 1.4, see Fig. 13). The smaller adult females probably mature sexually in their sixth year, but most probably do so when seven years old. Accordingly, some _T. spinifer emoryi_, which are sexually mature at a plastral length of 16.0 centimeters, are also sexually mature in their seventh year, whereas most _spinifer_ (sexually mature at a plastral length of 18.0 to 20.0 cm., corresponding to a length of carapace of 25.2 to 28.0 cm. or about 10 to 11 inches) probably become sexually mature in their ninth year, and some when eight years old. Most males of _spinifer_ are sexually mature when the plastron is 9.0 to 10.0 centimeters long (length of carapace 12.6 to 14.0 cm. or 5 to 5-1/2 inches), whereas males of _muticus_ and some _T. spinifer emoryi_ are sexually mature at a plastral length of 8.0 to 9.0 centimeters (length of carapace 11.2 to 12.6 cm. or 4-1/2 to 5 inches). The smaller adult males are probably sexually mature in their fourth growing season. Breckenridge (_op. cit._:7, Tab. II) commented on the abundance of females between five and 12 inches in length, and males that ranged in length from five to seven inches. The abundance of turtles in these size ranges is probably due, in part, to a slowing of the rate of growth indicating the approach of sexual maturity; the abundance of the smallest males is especially in accord with the size at sexual maturity of males (about five inches).

The largest acceptable record of size of _spinifer_ is 18 inches in length of carapace (Breckenridge, 1957:232). Stockwell (1878:402), however, wrote that females of _spinifer_ attain "an extreme length of from twenty-four to twenty-eight, and, in rare instances, thirty inches, with an average length of carapace of fifteen to eighteen," and True (1893:152) mentioned lengths of two feet or even more. Turtles 17 to 18 inches long are doubtless rare and probably about 60 years old. A specimen of _ferox_ lived the longest time in captivity--25 years (Pope, 1949:304). Individuals of _ferox_ probably exceed the maximum recorded length of carapace of 18-1/2 inches (Agassiz, 1857:401). The head of a _ferox_ having a width of 3-1/2 inches (Wright and Funkhouser, 1915:120) corresponds to a length of carapace of approximately 22-1/2 inches (PL/HW == 4.9; CL/PL == 1.3). De Sola and Abrams (1933:12) wrote that _ferox_ in the Okefinokee Swamp, Georgia, attains a length of two feet. The largest female of _muticus_ of which I have record is 21.5 centimeters in plastral length (KU 2308), a measurement corresponding to a carapace about 13 inches long.

Mortality

Man, in one sense or another, is a great enemy of soft-shelled turtles. Those caught by fishermen are destroyed because of the erroneous belief that they are harmful to fish populations. Some are drowned in hoop-nets or gill nets used by commercial fishermen. Many softshells are used by man for food. Herald (1949:118-19) reported the results of spraying an area with DDT and mentioned a 10-inch individual of _ferox_ that was eating a dead bluegill, and which "probably died as a result of ingesting contaminated food."

Predation on eggs probably accounts for most mortality. Hamilton (1947:209) reported tracks of spotted skunks, raccoons and foxes seen about destroyed nests, and Cahn (1937:183) incriminated skunks and raccoons. Goldsmith (1945:449) reported a raccoon that unearthed seven nests in one night. Little and Keller (1937:221) wrote of egg shells found in the sand (probably not as a result of hatching), and Muller (1921:182) reported egg shells around dug-up nests, suggesting such predators as "ground moles," raccoons and crows. Chesser (_in_ Harper, 1926:416) said that in the Okefinokee Swamp the jackdaw (fish crow), raccoon, bear and domestic dogs will eat the eggs. Wright and Funkhouser (1915:122) recorded a young _ferox_ in the stomach of a water moccasin (_Agkistrodon piscivorus_), and suggested that young soft-shells probably are food of larger snakes. Kellogg (1929:26) wrote that stomachs of two alligators each contained one soft-shelled turtle. Newman (1906:136) found that young captives were eaten by individuals of _Chrysemys_ and _Sternothaerus_, and I found that they were eaten by _Kinosternon_. Mitsukuri (1905:261-62) stated that first- and second-year individuals of _T. sinensis_ are eaten by the adults.

Breckenridge (1960) wrote that a clutch of eggs probably failed to develop because of an "... unusually cool season." Evermann and Clark (1920:595) stated that "many young appear to perish during the first winter." They (_op. cit._:594) found two eggs submerged in two feet of water and it is supposed that they never hatched. Dundee (1950:139) reported remains of soft-shelled turtles left on the mud of a dried swamp.

Parasites

Muller (1921:182) found maggots in a few eggs of a clutch, but thought that only the infertile and decomposing eggs were infested. I removed a hard, spherical cyst from the hind leg of a preserved softshell (TU). A captive hatchling (TU 17304) died as the result of a continuously enlarging and deepening hole on the top of its head; I could not discern a visible parasite with the naked eye. I found 25 leeches (_Placobdella parasitica_, largest about 13 mm.; identified by Dr. Kenneth B. Armitage, Department of Zoology, University of Kansas) in association with 11 _T. m. muticus_ (number per turtle not known) that were collected from the Kansas River at Lawrence, Douglas County, Kansas. Evermann and Clark (1920:596) reported a few nematodes in the stomachs of some _spinifer_, and three nematodes are listed by Harwood (1932:46, 60, 62, 66) in the same species. Hughes, Higginbotham and Clary (1941) have listed the known reptilian hosts of parasitic trematodes, and Hughes, Baker and Dawson (1941) have done the same for tapeworms. The species of parasites and their trionychid hosts are listed below.

TREMATODA _Trionyx ferox_: _Neopolystoma orbiculare_ _Vasotrema amydae_ _Neopolystoma rugosa_ _Vasotrema attenuatum_ _Polystomoides coronatus_ _Vasotrema robustum_ _Teloporia aspidonectes_

_Trionyx muticus_: _Crepidostomum cooperi_ _Opisthorchis ovalis_

_Trionyx spinifer_: _Hapalorhynchus evaginatus_ _Vasotrema amydae_ _Opisthorchis ovalis_ _Vasotrema attenuatum_ _Polystomoides coronatus_ _Vasotrema longitestis_ _Teloporia aspidonectes_ _Vasotrema robustum_

CESTODA _Trionyx ferox_: _Proteocephalus trionychinus_

_Trionyx spinifer_: _Proteocephalus testudo_

NEMATODA _Trionyx spinifer_: _Camallanus trispinosus_ _Spiroxys amydae_ _Falcaustra chelydrae_

Economic Importance

Several authors have mentioned softshells as a food item much sought after by man. The commercial value of these turtles has been summarized by Clark and Southall (1920:15-16). Softshells are consumed in quantity only in small towns near the place of capture. They are found only occasionally in the markets of large cities because the turtles are little known and the palatability of their flesh is unappreciated. Also, they do not stand shipment so well as other turtles, and they are "not so meaty as the snapper; so there is more waste" (Clark and Southall, _loc. cit._). Little and Keller (1937:221) reported living individuals for sale at the market in Ciudad Juarez, Chihuahua; however my inquiry at markets in Juarez in the summer of 1959 disclosed no evidence of recent sale of soft-shelled turtles. In the southeastern United States the demand is perhaps greater than in other regions. I have noted softshells in the market at New Orleans, and Oliver (1955:19) has mentioned the sale of "some 146,600 pounds" in one recent year in Florida. Over most of their range, however, there probably is no general demand for softshells and no special efforts are made to capture them. Softshells have been raised successfully on "turtle farms" in Japan (Mitsukuri, 1905). True (1893:152) wrote that "The eggs also are considered very excellent."

Softshells generally are condemned by fishermen because of the mistaken belief that they are detrimental to fish populations. Food of softshells is principally crawfish and insects. Fish comprise a small proportion of the diet (frequency 1.9% in Michigan, Lagler, 1943: Tab. 9). Most of the fishes eaten seem to be small minnows. Probably fish would comprise a larger percentage of the diet if they could be caught. I doubt that a softshell can pursue and capture a healthy fish in natural waters. Recently dead fish are eaten and perhaps fish eggs, and senile and decrepit fishes. There is no evidence that soft-shelled turtles are active predators on any kind of fish. Of course in congested areas such as ponds of fish hatcheries, it is desirable to eliminate the turtles. The known food habits of soft-shelled turtles suggest that they compete with game fishes for food, but there is no information on the intensity of competition (Lagler, _op. cit._:305).

The combined statements of many authors in their general accounts of food habits (for instance, Babcock, 1919:425) have tended to create the erroneous belief that soft-shelled turtles harm waterfowl. To my knowledge the only basis for this belief is the statement of Wright and Funkhouser (1915:123) that according to the natives of the Okefinokee Swamp, the larger turtles "devour also such waterfowl as are unfortunate enough to be taken unaware by these reptiles." Perhaps an occasional waterfowl is eaten, but the present information on kinds of food eaten certainly does not warrant the destruction of soft-shelled turtles. There may be some mortality in congested areas such as game refuges where young birds crowd the surface of the water.

The kind of bait successfully used in trapping softshell turtles suggests that they are of some value as scavengers.

EVOLUTIONARY HISTORY

Before attempting to reconstruct the history of soft-shelled turtles in North America, it will be helpful to summarize the salient facts concerning the distribution and relationships of the living forms, and to comment on fossils.

Distribution

The geographic range of the family Trionychidae in North America is principally in the eastern two-thirds of the continent and contributes to the well-known floral and faunal resemblance of eastern North America to that of eastern Asia (Schmidt, 1946:149) because _Trionyx ferox_ (see Fig. 18) resembles the species of the genus in Asia more closely than it does any North American species. The Recent distribution in America does not include the Neotropical region, whereas the geographical range in the Old World extends south of the equator (Fig. 1; Dunn, 1931:109, fig. 2; Gadow, 1909:333, fig. 72; Hay, 1908:35, fig. 16).

American softshells occur in all river systems in the United States and the two adjacent river systems on the east coast of México that drain into the Gulf of México. Softshells inhabit streams of the Great Plains and occur westward to the foothills of the Rocky Mountains in the western tributaries of the Mississippi River. Only _T. s. spinifer_ occurs in the southern part of the Great Lakes-St. Lawrence drainage. Softshells are absent from the Atlantic Coast drainage except the Hudson River and those rivers at least south of (and including) the Pee Dee River in South Carolina.

_T. s. emoryi_ is not known to be indigenous west of the Río Grande drainage, and has probably been introduced across the Continental Divide via the Gila River in western New Mexico into the Colorado River drainage of Arizona (Miller, 1946:46); the species undoubtedly occurs in México on the Sonoran side of the Colorado River opposite Baja California (Bogert and Oliver, 1945:417).

In the summer of 1959, I trapped turtles and with a specimen in hand inquired about softshells occurring in the inland drainages of northern México. From two collecting stations on the Río Nazas in Durango, only specimens of _Pseudemys_ and _Kinosternon_ were obtained; local inhabitants had neither seen nor heard of softshells. Flooded conditions in August of 1959 permitted trapping in only one of the inland drainages of northwestern Chihuahua, the Río Santa María; only specimens of _Kinosternon_ were obtained. Local residents near that river as well as those living near the Río Casa Grandes and Río del Carmen had not seen or heard of softshells. A person that I judge to be a competent observer reported seeing a softshell in June of 1958 in the Río Alamos (Arroyo Cuchujáqui) near Alamos, Sonora, in the Río del Fuerte drainage on the west coast of México. I was a member of a field party from the University of Kansas that visited that locality in late January of 1959; only specimens of _Pseudemys_ and _Kinosternon_ were collected. Possibly isolated populations occur in streams of the Pacific Coast drainage of northern México. If so, they may have entered Pacific Coast drainages by stream capture across the Continental Divide. Several species of fish that are characteristic of the Río Grande traversed the Sierra Madre Occidental at some former time (presumably via the Río Conchos and Río Papigochic) and occur in the Yáqui River drainage (Meek, 1904:xxxviii, xlvii; Miller, 1959:214-15, 217). Because of the probability that the Río Nazas at some former time flowed north into the Río Grande (Meek, _op. cit._:xxxiv), it is notable that softshells are absent in the Río Nazas drainage; the Big Bend turtle, _Pseudemys scripta gaigeae_, occurs in both drainages.

Relationships

Characters of _Trionyx ferox_ suggesting a closer resemblance to some Old World members of the family than to the other three American species are: large size; marked difference between juvenal and adult patterns on the carapace; the marginal ridge; and the longitudinal ridgelike prominences on the carapace, especially in juveniles. Other characters of _ferox_ suggesting a corresponding, but less marked resemblance to Old World species of _Trionyx_ are: the large size of the eighth pair of pleurals; the absence of callosities on the epiplastron and preplastra; frequent fusion of the hyoplastra and hypoplastra (more than in _spinifer_ or _muticus_); and tolerance of marine waters (more than _muticus_ or _spinifer_). Some fossils also suggest alliance with _ferox_ and some Old World members of the genus in their large size, large eighth pair of pleurals, and occurrence in marine deposits; several Old World species have been reported at sea (_Pelochelys_, _T. triunguis_, _T. sinensis_). _T. ferox_ is monotypic and has the most southeasterly displaced, geographic range.

Because _ferox_ resembles softshells from the Old World more closely than it does any American species, _ferox_ is assumed to be more closely related to Old World softshells than to any American species, and, because of resemblance to some fossils, _ferox_ is assumed to resemble most closely the primitive, ancestral stock of softshells that occupied North America. _T. spinifer_, _T. muticus_ and _T. ater_, which resemble each other more closely than any of them resembles _T. ferox_ or any Old World species, are considered autochthonous in North America. _T. spinifer_ and _T. muticus_ are distinct, sympatric species. Burt (1935:321) suggested that the two species "may be variants of the same species." _T. ater_ is weakly differentiated from _T. spinifer emoryi_. The species, _ferox_, _spinifer_ and _muticus_ are well-differentiated and were considered by Agassiz (1857), Gray (1869) and Baur (1893) as belonging to three different genera.

In the widely distributed _T. spinifer_, the subspecies _spinifer_, _hartwegi_ and _asper_ closely resemble one another; _asper_ seems most distinct, whereas _spinifer_ and _hartwegi_ are terminal populations of an east-west cline in one character. The subspecies _pallidus_, _guadalupensis_ and _emoryi_ resemble one another more closely than any resembles any of the subspecies mentioned immediately above; _T. s. pallidus_, however, is annectent. _T. s. pallidus_ and _guadalupensis_ represent terminal populations of clines in several characters, some of which occur in _emoryi_, but that subspecies is more distinct from _pallidus_ and _guadalupensis_ than those subspecies are from each other. _T. s. emoryi_ is the most variable subspecies. _T. ater_, known only from a restricted area in central Coahuila, is most closely related to _T. s. emoryi_, and possesses some characters judged to represent the attenuation of the geographic cline in _pallidus_, _guadalupensis_ and _emoryi_ mentioned above. Some characters of _ater_ show alliance to the species _muticus_. Of _T. muticus_, whose geographic range is removed from that of _ater_, there are two subspecies. Four subspecies of _spinifer_ (_spinifer_, _hartwegi_, _pallidus_ and _asper_) intergrade in the Mississippi River drainage of Louisiana; few specimens, however, are typical of _asper_. The subspecies of _muticus_ do not show definite evidence of intergradation. To facilitate quick reference, the occurrence of some characters that are shared by, or are approximated in, two or more forms are listed in Table 10. In addition to external characters, some ratios emphasize the clinal relationship between _T. s. pallidus_, _guadalupensis_, and _emoryi_ mentioned above. Of especial interest is the frequent resemblance of those subspecies and _T. ater_ to _T. ferox_ (dorsal pattern on limbs of adults, reduction in anterior tuberculation, wide head, narrow carapace, and short snout), and the less marked resemblance of _T. muticus_ to _T. ferox_; not shown in Table 10 is the resemblance of _ferox_ to _T. muticus calvatus_ in having thick, black-bordered postocular stripes. Some populations of _T. s. emoryi_ resemble _T. muticus_ in the corresponding size at sexual maturity and in having well-developed plastral callosities. It is notable that the occurrence of _ater_, and to a lesser extent that of _T. s. emoryi_, which resembles _ferox_ (and _muticus_), is in the southwestern United States and northern México.

TABLE 10. Frequency of Selected Characters Among Species and Subspecies of Trionyx in North America. Characters of muticus Refer to the Typical Subspecies; Horizontal Dashes Connecting X's Indicate that Computations for Those Subspecies Were Combined; Vertical Dashes Indicate that the Subspecies Is Intermediate Between the Adjacent Subspecies.

Column headings:

A: _ferox_ B: _spinifer_ C: _hartwegi_ D: _asper_ E: _pallidus_ F: _guadalupensis_ G: _emoryi_ H: _ater_ I: _muticus_

=====================================+=================================== | Species and subspecies Characters +---+---+---+---+---+---+---+---+--- | A | B | C | D | E | F | G | H | I -------------------------------------+---+---+---+---+---+---+---+---+--- Juvenal pattern: | | | | | | | | | black spots, ocelli | | X | X | X | | | | | | | | | | | | | | white dots | | | | | X | X | X | X | -------------------------------------+---+---+---+---+---+---+---+---+--- Pattern on snout: | | | | | | | | | acute angle (reduced in _muticus_) | X | X | X | X | X | | | | X | | | | | ¦ | | | | triangular | | | | | X | X | X | X | -------------------------------------+---+---+---+---+---+---+---+---+--- Pattern on side of head: | | | | | | | | | contrasting marks | X | X | X | X | X | X | | | | | | | | | ¦ | | | non-contrasting marks (distinct | | | | | | ¦ | | | stripe in _muticus_) | | | | | | X | X | X | X -------------------------------------+---+---+---+---+---+---+---+---+--- Pattern on limbs of adults: | | | | | | | | | contrasting | | X | X | X | X | X | | | | | | | | | ¦ | | | reduced or absent | X | | | | | X | X | X | X -------------------------------------+---+---+---+---+---+---+---+---+--- Tuberculation (anterior edge of | | | | | | | | | carapace): | | | | | | | | | conical, equilateral | | X | X | X | X | | | | | | | | | | | | | reduced or absent | X | | | | | X | X | X | X -------------------------------------+---+---+---+---+---+---+---+---+--- Head (PL/HW, fig. 3): | | | | | | | | | wide | X | | | X | | X | X | X | | | | | | | | | | narrow | | X | X | | X | | | | X -------------------------------------+---+---+---+---+---+---+---+---+--- Carapace (CL/CW, fig. 4): | | | | | | | | | wide | | X | X | X | X | X | | | X | | | | | | ¦ | | | narrow | X | | | | | X | X | X | -------------------------------------+---+---+---+---+---+---+---+---+--- Level of Carapace Width (CL/PCW, | | | | | | | | | fig. 5): | | | | | | | | | middle of carapace | X | X | X | X | | | | | X | | | | | | | | | farther posteriorly | | | | | X | X | X | X | -------------------------------------+---+---+---+---+---+---+---+---+--- Snout (HW/SL, fig. 6): | | | | | | | | | long | | X---X | X | X---X | | | X | | | | | ¦ ¦ | | | short | X | | | | X---X | X | X | -------------------------------------+---+---+---+---+---+---+---+---+---

Fossils

The known occurrence of fossil trionychids throughout the world indicates a former distribution more widespread than the family has today; the principal difference in the former and present distributions is the lack of living softshells in Europe.

I have not studied in detail the many fossil remains but such examination as I have made of them suggests that many of the characters used as a basis for distinguishing fossil forms in North America are subject to individual variation or are of no diagnostic value in the living species (Hummel, 1929:769). Knowledge of the variation in the living species of the Old World would aid in adequately appraising the North American fossils. Some osteological characters of the three living American species (excluding _ater_) together with data on variation within a given species are mentioned below. Some differences in skulls of the three species already were mentioned in the section "Osteological Characters." Because most fossil remains are those of the carapace and plastron, attention is here given to those structures.

_Widened alveolar surfaces of jaws._--An ontogenetic variation affecting large skulls of _T. ferox_ and some individuals of _T. spinifer asper_; presumably confined to females. Of especial interest is its presence in some populations of _asper_ that are not otherwise distinguishable (external characters) from the rest of the individuals comprising that subspecies.

_Sculpturing._--No differences in pattern (generally of anastomosing ridges) on carapace or plastron; fineness or coarseness seemingly correlated with size; frequency and kind (knoblike or ridgelike) of bony prominences on carapace variable; bony prominences confined to species _spinifer_ and _ferox_, occurring principally on large females.

_Fontanelles of carapace._--Closure more or less correlated with increasing size, although much variation noted between individuals of same size; small individuals have fontanelles confluent (medially), thus separating nuchal from contact with first neural and first pair of pleurals.

_Number and arrangement of neurals and pleurals._--Neurals number six to nine, usually seven or eight; pleurals number seven or eight pairs, and may or may not be in contact with each other posteriorly; eighth pair of pleurals when present reduced, never contacting seventh neural; arrangement posteriorly variable (see Fig. 16 and Tab. 5).

_Plastral callosities._--Increase in size with advancing age causing corresponding reduction in size of plastral vacuity; relatively best developed in _muticus_ (all elements touching medially on KU 41380 leaving no plastral vacuity); probably no callosities on preplastra or epiplastron of _ferox_; callosity on epiplastron of _spinifer_ not covering entire surface (as it may in _muticus_).

_Epiplastron._--Obtusely-angled (greater than 90 degrees) in _muticus_; acutely-angled (90 degrees or less) in _ferox_ and _spinifer_.

_Hyo-hypoplastral suture._--Usually present, but occasionally absent, in all species.

The fossil turtles of North America have been treated monographically by Hay (1908), who apportioned fossil trionychid remains into eight genera (three living) of two families. Recently, Romer (1956:514) relegated all trionychid fossils to the genus _Trionyx_. Characters, as gleaned from Hay's synopsis (_op. cit._:465-548, Pls. 85-113), that seem especially worthy of taxonomic consideration are: (1) The presence of a preneural, which is not known to occur in the living American species (seemingly the preneural is fused with the first neural and represents the elongate first neural in living species); (2) The large eighth pair of pleurals, especially when they contact the seventh neural; (3) The thickness of the costal plates, a condition probably correlated with the size of some fossils, which are larger than any living species (for example, Hay, _op. cit._:518, mentioned the greatest dimension of a nuchal bone as approximately 300 mm.).

The approximate extent of the known horizontal distribution of fossils is indicated in Figure 24. A comparison of known localities of fossils and the distribution of living softshells (introduced population of _T. s. emoryi_ in Colorado River drainage omitted) shows that the distribution was more widespread in former times. Localities of fossils are centered on the Atlantic Coast from New Jersey to North Carolina and in the Rocky Mountain-Great Plains region from Alberta and Saskatchewan to northwestern New Mexico; the oldest fossils, which occur in each region, are found in Upper Cretaceous deposits. Many fossils occur in marine and brackish water deposits. Most localities depicted on the map are mentioned by Hay (1908:36-37, 465-548). Other localities included on the map are in southern Alberta (Russell, 1929:164; 1930:27; Sternberg, 1926:104), southern Saskatchewan (Russell, 1934:109), northern South Dakota (Hay, 1910:324), central Utah (Gilmore, 1946), western Colorado (Schmidt, 1945), southwestern Kansas (Galbreath, 1948:284), southeastern Texas (Hay _in_ Stejneger, 1944:65), southern California (Brattstrom, 1958:5), and northeastern Coahuila, México (Mullerried, 1943:623). Hay's record of the living _Platypeltis_ (= _Trionyx_) _ferox_ and other remains from the Peace Creek formation in Hillsborough County, Florida (_op. cit._:548), presumably is the same record mentioned by Pope (1949:305).

Ameghino (_in_ Hay, _op. cit._:35) recorded specimens of a trionychid from the Cretaceous of Patagonia, a record that, at present, cannot be accepted (Simpson, 1943:423). Mullerried (_loc. cit._) also mentioned some trionychid remains that were housed in Tuxtla Gutierrez, Chiapas, México, (material now lost), but their geographical provenance was unknown. The former extent of range southward is not known; it is improbable that trionychids occurred in South America (Simpson, 1943:423).

Phylogeny

The occurrence of _T. ferox_ in Florida and the suggestion of _ferox_-like characters in turtles from southwestern Texas and northern Mexico presents a distributional pattern that resembles the disjunct ranges of many other pairs of closely related taxa. The clear-water ponds in central Coahuila, which are inhabited by _ater_, correspond to aquatic habitats supporting _ferox_ in Florida. The splitting of the geographic range into eastern and western parts possibly resulted from a southward shift of colder climates in glacial stages of the Pleistocene, or from the development of an intervening arid region in the late Miocene and Pliocene (see discussions in Martin and Harrell, 1957, and Blair, 1959). An initial separation of range by an arid environment in the Pliocene may have been terminated by the colder climates in the Pleistocene.

The degree of morphological difference between _ferox_ and the forms in southwestern Texas and northern México, suggests that the time of separation antedated the Pleistocene.

Trionychid turtles may have traversed the Bering land bridge between Asia and North America in late Mesozoic times for they occur as fossils on the Atlantic Coast and in the Rocky Mountain-Great Plains region in Upper Cretaceous deposits. Shallow, inland seas may have afforded no barrier to the dispersal of softshells which presumably were tolerant of saline waters. The orogeny and volcanic action with subsequent erosion and sedimentation of the Rocky Mountain system, which was later accompanied by drier climates, tended to obliterate suitable habitats in the western United States; softshells persisted at least until the Upper Eocene on the west coast (Brattstrom, 1958:5). The factors responsible for the disappearance of softshells on the Atlantic Coast probably were related to the glacial advances in the Pleistocene; the most recent fossils known occur in Miocene deposits.

The relationships of the living species and subspecies were probably correlated with geologic change in aquatic environments and drainage patterns. These changes probably included stream capture, flooding, drought, uplifting and planation. A hypothetical, evolutionary history is presented in the phylogenetic diagram where letter symbols represent species and subspecies, and grouped symbols (referred to in subsequent paragraphs) represent ancestral stocks.

Pliocene Pleistocene Recent ==========================================================================

+--F-----------------------------------F (_ferox_) | | +---------Mm (_muticus muticus_) | +--M------------------+ | | +---------Mc (_muticus calvatus_) | | FMSA-+ | +--Ss (_spinifer spinifer_) | | +------+ | | | +--Sh (_spinifer hartwegi_) | | +--Ssha-+ +--MSA-+ | | | | +---------Sa (_spinifer asper_) | | | +--S---+ +--Sp (_spinifer pallidus_) | | | +--Spg-+ | | | | +--Sg (_spinifer guadalupensis_) +--SA--+ +--Sepg-+ | | | +--Se-----Se (_spinifer emoryi_) | +--A---------------------A (_ater_)

--------------------------------------------------------------------------

An arid environment in the central and southern United States and northern Mexico may have increased in area especially southward from Miocene times into the Pliocene (Dorf, 1959:189, 191). The combination of physiographic changes and aridity, which modified the mesic, essentially continuous, aquatic habitats, may have isolated and aided in the differentiation of the _ferox_, _muticus_ and _spinifer_ stocks. Encroachment of the Eocene seas, the maximal extent of which corresponded to the Gulf Coastal Plain and included a northerly extension as far as Cairo in southern Illinois (Mississippi embayment), possibly was an initial barrier isolating the _ferox_ stock of the east.

In the late Miocene or early Pliocene, the MSA (_muticus-spinifer-ater_) stock presumably occupied a large region of the central United States, which extended southward into northern México and along the Gulf Coast at least as far as Alabama. Farther eastward, the _ferox_ stock was isolated in more mesic, probably swampy, marshy habitats.

Later, in the southwestern part of the range of the MSA stock (southern Texas and northern México), the SA and _muticus_ stocks were separated. The _muticus_ stock occurred to the northeastward, and presumably no farther south than the area included within the present drainage basin of the Colorado River. Southward, the SA stock was isolated into several populations that are today represented by _ater_ and _T. s. emoryi_, the most variable subspecies; the distribution of the most distinctive population of _emoryi_ indicates a former isolated inland drainage. The multiple fragmentation of the SA stock presumably terminated by the end of the Pliocene. The progenitors of _T. ater_ probably closely resembled _ferox_. _Trionyx ater_ and _T. ferox_ resemble each other morphologically and in habitat. Therefore, the progenitors of _ater_ are considered to have undergone comparatively little differentiation.

The _spinifer_ stock, occurring principally in the area included within the present drainage basin of the Río Grande, extended its geographic range eastward and became sympatric with _muticus_ and _ferox_. An expansion of range necessarily demands more mesic conditions; these were perhaps afforded by the pluvials (wet, rainy ages) that were coincident with the glacial periods in the Pleistocene (Antevs, 1948:168). The pluvials permitted the isolated populations of the _spinifer_ stock to unite, and permitted that stock to extend its range eastward. The concurrent continental glaciation permitted the _spinifer_ stock to extend its range eastward only in a belt approximately 300 miles wide along the Gulf Coast, and also displaced the ranges of _ferox_ and _muticus_ to southern latitudes. Perhaps _ferox_ was less tolerant of decreased temperatures or changes in habitat than was the _spinifer_ stock but, for some unknown reason, _ferox_ did not extend its range westward. Because _T. ater_ closely resembles _T. s. emoryi_, continued isolation of _ater_ since the beginning of the Pleistocene seems unlikely and _ater_ may have been reunited in subsequent pluvial periods with the _spinifer_ (_emoryi_) stock. A climatic fluctuation between relatively wet and dry periods is corroborated by studies of soil profiles in Trans-Pecos Texas (Bryan and Albritton, 1943).

The separation of the range of _spinifer_ in the general region of western Louisiana, resulting in the differentiation of the _spinifer_ group of subspecies to the east and the _emoryi_ group of subspecies to the west, and the differentiation of _T. s. asper_ and _T. m. calvatus_, both having corresponding western limits of distribution (Mississippi River drainage), are associated with the activities of the Mississippi River and its flood-plain. The combined effects of the pluvials and interpluvials seem responsible for changes in the lower Mississippi Valley. Great volumes of summer melt-water in the glacial stages greatly increased the breadth of the channel of the lower Mississippi River (corresponding to the northern extent of the Mississippi embayment; Hobbs, 1950), and this, coupled with the encroachment of Pleistocene seas (especially in the Mississippi embayment) in the interglacial periods, perhaps separated populations eastward represented today by _T. m. calvatus_ and _T. s. asper_. The _spinifer-hartwegi_ stock probably developed in southern Louisiana in association with the meandering of the Mississippi River and its tributaries, and its broad alluvial plain. The biota of that plain differed from that adjacent to the east or west (see discussion in Viosca, 1944) and constituted a barrier, of a sort, to free communication between the east and west. Westward the _emoryi_ group of subspecies differentiated, its eastern limit probably being the Red River, which followed its own course to the Gulf along the lowlands on the west side of the Mississippi Valley and did not empty directly into the Mississippi until Recent times (Holland, 1944:20). There was not an equally-marked, corresponding separation of the range of _muticus_. However, the juvenal pattern of the subspecies _muticus_ that inhabits the Gulf Coast streams is slightly different (having less short lines) from that of _muticus_ elsewhere.

The Río Grande (inhabited by _emoryi_) presumably had its own exit to the Gulf whereas rivers westward to (and including) the Red River (inhabited by _pallidus-guadalupensis_ cline) probably were joined near their mouths forming a large drainage system. Hubbs (1957:93) pointed out that the Río Grande-Nueces divide also limits a large number of species of fish. The differentiation of _pallidus_ and _guadalupensis_ is possibly due to a difference in the salt content of waters that drain the Edward's Plateau (see page 547), or to isolation of those subspecies in separate drainage systems that had their own exits to the Gulf.

In the lower Mississippi drainage, the _spinifer-hartwegi_ stock extended its range northward following the retreat of the last glacial stage, and differentiated into those two subspecies in the upper Mississippi drainage and Great Lakes-St. Lawrence drainage system.

I have seen one specimen (UMMZ 59198) from the eastern part of the Tennessee drainage (inhabited by _T. s. spinifer_) that resembles _T. s. asper_ (occupying the Gulf Coast drainages of the southeast). This resemblance tends to support the thesis of a former confluence of the Coosa (Alabama River system) and Tennessee drainages as believed by some malacologists to explain resemblances in molluscan fauna and as corroborated by physiographical evidence (see discussion in van der Schalie, 1945).

The Importance of the Study of Turtle Populations in Relation to the History of River Systems

In the Río Grande drainage the geographic distribution of the population of _emoryi_ having orange color in males is approximately the same as that of _Pseudemys scripta gaigeae_; the corresponding distributions suggest that a part of the Río Grande drainage consisting of the Río Conchos in Chihuahua and the Big Bend region of Texas was isolated in former times. Accordingly, the known aquatic chelonian fauna in the basin of Cuatro Ciénegas in central Coahuila, México, is endemic (except _T. s. emoryi_). And the coincidence of the geographic ranges of _T. muticus calvatus_ and _Graptemys pulchra_ in the southeast suggest a former association of the included (Pearl to Escambia) river systems. The occurrence of _T. s. pallidus_ in the Red River drainage indicates that the Red River was formerly associated with the Gulf Coast streams of eastern Texas and western Louisiana (inhabited by _pallidus_) and not with the Mississippi River drainage. The lower Mississippi River valley forms a prominent barrier to the eastern and western dispersal of many kinds of species and subspecies of turtles. _T. m. calvatus_ and _T. s. asper_, which occur in rivers of the Gulf Coast drainage east of the Mississippi, are well-differentiated subspecies showing little or no evidence of intergradation with their relatives in the Mississippi River. The large faunal break provided by the Mississippi River would seem to indicate greater age for that river than for other rivers of the Gulf Coast drainage.

A comparison of the distributions of _Trionyx_ and _Graptemys_ in Texas suggests a faunal break between the drainage systems of the Brazos and Colorado rivers. _Graptemys versa_ occurs in the Colorado and Guadalupe-San Antonio drainages. To my knowledge _versa_ hitherto has not been recorded from the latter drainage system. I have seen one specimen of _Graptemys_ (custody of Gerald Raun, University of Texas) from the Guadalupe River drainage, which I judge to be representative of _versa_, and Olson (1959:48) has reported _Graptemys_ (probably _versa_) in the San Antonio River. The distribution of _G. versa_ parallels in a general way, the distribution of _T. s. guadalupensis_. _G. kohni_ and _T. s. pallidus_ occur in the Brazos River and eastward. Also, it is notable that the population of _T. m. muticus_ occurring in the Colorado River drainage differs slightly (more black pigmentation) from the same subspecies in the adjacent Brazos River system.

There is much difference in the patterns of distribution and degree of differentiation of different genera of aquatic turtles in the eastern United States. Tinkle (1958:41-43, Figs. 49-55) concluded that a general resemblance in the patterns of distribution of the different genera of turtles was evidence that the rates of evolution were essentially the same, assuming that each genus had had a similar time interval for differentiation (_op. cit._:42). If this is true, corresponding patterns of distribution might indicate the same relative age of the population of turtles concerned. Generally, the genera of turtles that on morphological grounds are considered the oldest and most primitive (_Macroclemys_, _Chelydra_) show less differentiation into species and subspecies than those considered younger and more recently evolved (_Graptemys_, _Pseudemys_). In the genus _Graptemys_, much differentiation occurs in the geologically, recently formed, Gulf Coast drainage systems of the southeastern United States. It would seem then, that faster rates of differentiation denote more recent genera, whereas older genera are endowed with a "genetic senility" and are less subject to change.

Evidence of the relative age of two genera of turtles, as suggested by their degree of differentiation into minor taxa, and the degree of difference between populations of two genera that inhabit adjacent drainage systems, may indicate the relative ages of particular river systems. For example, the slight resemblance of _G. versa_ to _kohni_ and the close resemblance of _T. s. guadalupensis_ to _pallidus_ in Texas may reflect the age of the genus _Trionyx_ and the youth of the genus _Graptemys_. Remembering that the genus _Graptemys_ is relatively recently evolved and assuming _G. versa_ to be the most primitive and ancestral species of the genus (at least it is monotypic, the most aberrant species, and unlike any other species of the genus), it seems logical to suppose that the physiographic changes responsible for the Colorado-Brazos divide and the isolation of _versa_ occurred early in the evolutionary history of the genus _Graptemys_. The degree of differentiation of _Trionyx_ suggests that that genus is, comparatively, much older, and that the same physiographic changes responsible for the Colorado-Brazos divide and differentiation of the subspecies _pallidus_ and _guadalupensis_ occurred late in the evolutionary history of the genus _Trionyx_.

In general, patterns of distribution of turtle populations support physiographic evidence concerning changes in stream confluence and relative age of river systems.

SUMMARY

In North America, soft-shelled turtles (genus _Trionyx_) occur in northern México, the eastern two-thirds of the United States, and extreme southeastern Canada. The genus fits the well-known Sino-American distributional pattern. In North America there are four species. Three (_ferox_, _spinifer_ and _muticus_) are well-differentiated and one (_ater_) is not well-differentiated from _spinifer_. Characters of taxonomic worth are provided by the following: size; proportions of snout, head and shell; pattern on carapace, snout, side of head, and limbs; tuberculation; sizes of parts of skull; number of parts of carapaces; and, shape and number of some parts of plastra. Many features show geographical gradients or clines. _T. ferox_ is the largest species and _muticus_ is the smallest. Females of all species are larger than males. With increasing size of individual, the juvenal pattern is replaced by a mottled and blotched pattern in females of all species; adult males of _spinifer_ retain a conspicuous juvenal pattern, whereas the juvenal pattern is sometimes obscured or lost on those of _ferox_ and _muticus_. The elongation of the preanal region in all males, and the acquisition of a "sandpapery" carapace in males of _spinifer_ occur at sexual maturity. There is a marked secondary sexual difference in coloration in a population of _T. s. emoryi_ (side of head bright orange in males and yellow in females). The sex of many hatchlings of _T. s. asper_ can be distinguished by the pattern on the carapace. Slight ontogenetic variation occurs in some proportional measurements. Large skulls of _ferox_ and some _asper_ (those in Atlantic Coast drainages) have expanded crushing surfaces on the jaws. Considering osteological characters, _muticus_ is most distinct; there is less difference between _ferox_ and _spinifer_ than between those species and _muticus_.

_T. ferox_ is monotypic, confined to the southeastern United States, and resembles Old World softshells more than it does any American species. The northern part of the geographic range of _ferox_ overlaps that of _T. s. asper_; there, the two species are ecologically isolated. _T. spinifer_ is polytypic, has the largest geographic range, and is composed of six subspecies, of which two are described as new (_pallidus_ and _guadalupensis_). The subspecies are divisible into two groups. One, the _spinifer_ group (_spinifer_, _hartwegi_ and _asper_) is recognized by a juvenal pattern having black spots or ocelli; _asper_ is the most distinctive and shows little evidence of intergradation in the lower Mississippi River drainage with the _spinifer-hartwegi_ complex, which, northward, is differentiated into two subspecies in which there is an east-west cline in size of the ocelli on the carapace. The _emoryi_ group (_pallidus_, _guadalupensis_, _emoryi_) is recognized by a pattern of white spots; _emoryi_ is most distinctive. Each of several characters behaves as a cline if traced from east to west through the three subspecies. _T. s. pallidus_ intergrades with the _spinifer-hartwegi_ complex in the lower Mississippi River drainage. _T. s. emoryi_ is the most variable subspecies; in its most notable population the males have orange coloration. _T. s. emoryi_ has been introduced into the Colorado River drainage of Arizona. _T. ater_ most closely resembles _T. s. emoryi_, but shows alliance with _T. muticus_ and _T. ferox_. _T. ater_ is confined to ponds of crystal-clear water in central Coahuila, México. _T. muticus_ is completely sympatric with _spinifer_, and is composed of two subspecies (_muticus_ and _calvatus_). _T. m. calvatus_ shows no evidence of intergradation in the lower Mississippi River drainage with _T. m. muticus_, corresponding somewhat to the relationship of _T. s. asper_ with the intergradient population of _T. spinifer_ in the Mississippi River.

Softshells have pharyngeal respiration and probably are incapacitated by rotenone. _T. ferox_ and the subspecies of _spinifer_ occur in a wide variety of fresh-water habitats; _muticus_ is more nearly restricted to running water (especially in the northern parts of its range) than _spinifer_, and may be less vagile than _spinifer_. _T. ferox_ is more tolerant of marine and brackish waters than are _muticus_ or _spinifer_. Small size and pallid coloration seem correlated with arid environments. The largest species (_ferox_) and the smallest population of _spinifer_ (resembling _muticus_) both occur in the southernmost part of the range of the genus. Diurnal habits include basking on shores or débris in water, floating at the surface, procuring food, and burrowing in shallow and deep water (no observations for _spinifer_ and _muticus_ in deep water). Softshells are principally carnivorous; the food consists mostly of crawfish and insects; there is evidence of cannibalism involving predation on first- and second-year-old turtles. The capture of food is triggered primarily by movement of prey; sight seems to be more important than smell to _Trionyx_ in capturing food. There is no indication of a food preference between species; enlarged crushing surfaces of jaws in some _ferox_ and _asper_ may be an adaptation for feeding on mollusks. Schools of fish are reported to follow softshells, and presumably acquire food that is dislodged by the grubbing and scurrying of the turtles on the bottom. Softshells are wary. They are good swimmers, and travel rapidly on land. The depressed body is an adaptation for burrowing and concealment. Permanent growths of algae do not occur on the dorsal surface of softshells. There is evidence of some nocturnal activity, and a general parallel in habits between trionychids and chelydrids. Softshells sometimes move overland; they move little in aquatic habitats. The normal annual period of activity of _spinifer_ in latitudes 40° to 43° is approximately five months from April into September, depending on the weather; they hibernate under a shallow covering of mud in deep water. The southernmost populations may be active throughout the year.

Males of _spinifer_ are sexually mature when the plastron is 9.0 to 10.0 centimeters in length (some when 8.0 long), whereas those of _muticus_ are sexually mature at 8.0 to 9.0 centimeters. In the mentioned size range, the smaller adult males are probably in their fourth growing season, and the larger males in their fifth. Most females of _spinifer_ are sexually mature at a plastral length of 18.0 to 20.0 centimeters and are probably in their ninth year; the smaller individuals probably are in their eighth. Females of _muticus_ are sexually mature when the plastron is 14.0 to 16.0 centimeters long. Most of these are seven years old but some are only six years old. Some large females contain immature ovaries. The near-maximum length of carapace of _spinifer_ is 18 inches, and such turtles are perhaps 60 years old; _ferox_ perhaps attains a length of two feet.

_T. ferox_ deposits eggs from late March to mid-July, whereas northern populations of _spinifer_ and _muticus_ usually deposit theirs from mid-June to mid-July. Sandy sites are preferred for nests, although movement to other sites occurs if the preferred sandy sites are submerged or otherwise rendered unusable. _T. muticus_ limits its nest sites to the open areas of sand bars and does not lay inland where it must traverse vegetated areas, as does _spinifer_. Nests of _ferox_ and _spinifer_ seem to differ from those of _muticus_ in being flask-shaped.

The seasonal reproductive potential is perhaps less in northern populations (averaging 20 eggs per clutch and only one clutch per season) than in southern populations (averaging about 10 eggs per clutch, but three clutches per season). Larger females deposit more eggs than smaller females. Eggs laid in northern latitudes are slightly smaller than those laid farther south. In any latitude the incubation period probably is at least 60 days. Hatchlings presumably leave nests at dusk, nighttime or dawn, and may winter over in eggs or nests.

Man is a great enemy of softshells. Predation on eggs probably accounts for most mortality. Physical conditions of the environment (overcrowding of nest sites, inadequate hibernation sites) and probably some kinds of parasitism contribute to mortality. Softshells are eaten locally and sometimes appear in the market of large cities, but over most of their range, there probably is no general demand and no special efforts are made to capture them. Fish, mostly minnows, comprise a small proportion of the diet. There is no evidence that softshells are active predators on any kind of fish, but their known food habits suggest that they compete with game fishes for food. Softshells are scavengers.

Fossil material was not studied in detail. The fossil softshells indicate a more widespread, former distribution. Some osteological characters and their variation in the living species are mentioned as an aid to future workers concerned with an assay of fossil remains. Fossils occur in marine, brackish and fresh-water deposits, and many are much larger than the living species; the oldest American fossils are of Upper Cretaceous age.

The interrelationships of the living species and subspecies suggest that the species _spinifer_, _ater_, and _muticus_ are derivatives of a _ferox_-like ancestor, and that they differentiated in North America; most differentiation occurs in southwestern Texas and northern México where characters of some populations indicate alliance with _ferox_. It is hypothesized that aridity in the late Tertiary effected specific differentiation by the modification and isolation of aquatic habitats. Pluvial periods in the Pleistocene provided for confluence of aquatic habitats and expansion of geographic ranges, and coupled with physiographic changes, conceivably caused or enhanced some of the subspecific variation.

LITERATURE CITED

References marked with an asterisk were not seen by the author.

ADAMS, M. S., and CLARK, H. F.

1958. A herpetofaunal survey of Long Point, Ontario, Canada. Herpetologica, 14(1):8-10, April 25.

ADLER, K. K., and DENNIS, D. M.

1960. New herpetological records from Ohio. Jour. Ohio Herp. Soc., 2(4):25-27.

AGASSIZ, L.

1857. Contributions to the natural history of the United States of America. Vol. I. Part II. North American Testudinata. Vol. II.