Part 11

The costæ are channels on the inside of the valve, closed, except in the middle where elliptical foramina, opening into the interior of the valve, give rise through their terminal margins to the two longitudinal lines on each side of the valve. The raphe begins as a groove in the side of the conical central nodule and continues as a cleft at right angles to the plane of the surface of the valve, in which case the raphe forms a single line; if the raphe is inclined to the valve surface, then two lines appear in projection, the upper and lower edges of the cleft. In some forms the surface of the edge of the raphe on one side is folded or grooved for a considerable distance, and the opposite edge is elevated into a ridge or {102}tongue fitting into the groove. In such cases it is possible, in projection, to see the upper or outer edges of the raphe, the lower edges and the edges of the tongue and groove, thus showing four lines; sometimes, when the tongue and groove do not meet, six lines. The so-called inner channel is the part of the raphe on the inside of the tongue, and the so-called exterior channel is the part of the raphe on the outside of the tongue. If, in addition to this formation of the raphe, the plane of cleavage changes toward the terminal nodules, the lines will cross each other and, when two are superimposed, disappear altogether. For the careful examination of the raphe it is necessary to employ large forms, and it is advisable to use nitrate of silver which remains in the raphe, and, as in slides mounted by Mr. F. J. Keeley, shows in a beautiful manner the entire outline of raphe and fissures. The terminal fissures owe their separation to the different directions taken by the two edges of the raphe on each side, one edge bending in a wide curve toward the end of the valve, showing two lines, the upper and lower edges of one side of the raphe when inclined to the plane of the surface, and the other edge of the raphe turning suddenly in an opposite direction and ending abruptly in a curve, giving rise to the appearance, by diffraction, of a punctum.

Pl. 40, Figs. 13, 14 and 15.

Endochrome consists of two chromatophores lying on the zones.

Pinnularia is usually divided into the Majores, or larger, and the Minores, or smaller forms, the latter being further divided according to their striæ. The following classification is chiefly that of Cleve.

_Majores._--Valve large, linear with parallel or slightly radiate striæ and broad axial area.

_Gracillimæ._--Valve small, striæ parallel or nearly so; axial area very narrow.

_Capitatæ._--Valve with capitate or rostrate ends; striæ radiate.

_Divergentes._--Striæ strongly radiate.

_Brevistriatæ._--Striæ short.

_Distantes._--Striæ distant.

_Tabellariæ._--Striæ radiate in the middle, strongly convergent at the ends.

_Marinæ._--Marine forms.

MAJORES

PINNULARIA MAJOR (KUETZ.) WM. SM.

Valve linear, usually slightly gibbous in the middle and at the ends; raphe oblique; axial area less than one-third the width of valve, convergent at the ends; striæ, 7 or 8 in 10 µ, radiate in the middle, convergent at the ends, crossed by a narrow band. L. ? to 300 µ.

Blue clay. Fresh water. Abundant at Middletown, Delaware Co. (T. C. Palmer).

Pl. 28, Fig. 4.

Fig. 9, Pl. 29, is one of a number of smaller forms which are difficult to determine, approaching P. viridis.

PINNULARIA MAJOR VAR. PULCHELLA N. VAR.

Valve strongly gibbous in the middle and gradually widened to the rounded ends; axial area broad, less than one-third the width of the valve, widened unilaterally in the middle; striæ, 7 in 10 µ, crossed by a band nearly as wide as the length of the costæ and scarcely distinct. L. 273 µ.

{103}The central nodule is scarcely evident, probably because it is not so thick as in other forms. The outline is near to that of N. mesogongyla and certain forms of N. nobilis, differing from the latter in the median line, striæ and band which is wider than that of P. latevittata var. domingensis Cl.

Hammonton Pond, N. J.

Pl. 28, Fig. 2.

A very beautiful form which I cannot find described or figured. It does not appear to be N. major var. turgidula Cl., which has a narrow band. In the fossil deposit from Hopkinton, N. H., valves occur similar in outline but smaller.

PINNULARIA NOBILIS EHR.

Valve slightly gibbous in the middle and at the ends; median line complex; striæ, 4 or 5 in 10 µ, slightly convergent or parallel at the ends, crossed by a band one-third as wide as the length of the striæ. L. ? to 350 µ.

Blue clay. Fresh water.

Pl. 28, Fig. 1.

PINNULARIA DACTYLUS EHR.

Valve broad, linear, slightly gibbous in the middle; ends broad, rounded; median line not complex, sinuous; striæ, 4 or 5 in 10 µ, crossed by a very broad band. L. ? to 300 µ.

_Navicula gigas_ A. S.

Blue clay. Fresh water.

Pl. 28, Fig. 3.

Forms occur which are with difficulty assigned to either nobilis or dactylus.

PINNULARIA DACTYLUS VAR. DARIANA (A. S.) CL.

Valve linear-lanceolate, obtuse; axial area broad, less than one-third the width of the valve; striæ, 6 in 10 µ, crossed by a broad band. L. 220 µ.

Absecon, N. J.

Pl. 29, Fig. 3.

PINNULARIA DACTYLUS VAR. DEMERARÆ CL.

Valve elliptical-lanceolate, with sub-cuneate ends; axial area lanceolate, broad in the middle; median line flexuose; striæ radiate throughout, 6 in 10 µ. L. 150 µ.

Blue clay.

Pl. 29, Fig. 10.

PINNULARIA GENTILIS (DONK.) CL.

Valve linear, with rounded ends; axial area about one-fourth the diameter of the valve; striæ radiate in the middle, convergent at the ends, 7 in 10 µ, crossed by a broad indistinct band.

Fresh water. Not common.

Pl. 29, Fig. 1.

PINNULARIA TRIGONOCEPHALA CL.

Valve linear, gibbous in the middle and at the cuneate ends; axial area wider between the middle and the ends, dilated to an elliptical space in the middle; striæ, 6 in 10 µ. L. 145 µ.

Blue clay.

Pl. 29, Fig. 8.

{104}PINNULARIA VIRIDIS NITZSCH

Valve linear-elliptical, with rounded ends; axial area narrow, widened in the middle; striæ, 6 to 7 in 10 µ, crossed by a band as wide as one-third the length of the striæ.

Common in fresh water.

Pl. 29, Fig. 2.

Quite variable in size. Approaches P. major by intermediate forms as in Fig. 9, Pl. 29.

PINNULARIA VIRIDIS VAR. FALLAX CL.

Valve linear, with rounded ends; axial area narrow, slightly widened in the middle; striæ sometimes unilaterally interrupted, nearly parallel, 10 in 10 µ.

Elm, N. J.

Pl. 29, Fig. 4.

In Fig. 2, Pl. 30, a form is represented which corresponds closely to Navicula viridis var. B, of Wm. Smith. It is given as synonymous with var. fallax; it is bilaterally interrupted. Blue clay.

PINNULARIA VIRIDIS VAR. ?

Valve linear-elliptical, with rounded ends; axial area narrow, widened in the middle to a transverse fascia which is sometimes unilateral; striæ, 14, in the middle, divergent, convergent at the ends and closer, crossed by a narrow band. L. 45-60 µ. Fascia sometimes absent or very narrow.

Northbrook, Pa.

Pl. 30, Fig. 17 (represents a form with wider area than usual).

PINNULARIA VIRIDIS VAR. CAUDATA N. VAR.

Valve elliptical-lanceolate, with sub-rostrate ends; axial area narrow, widened to an orbicular space in the middle; striæ radiate in the middle, 11-12 in 10 µ, convergent and closer at the ends, crossed by a narrow band; median line with very long terminal fissures; terminal nodules noticeable because of the thickening of the edges of the terminal striæ. L. 43 µ.

Fresh water, Newtown Square. Not common.

Pl. 30, Fig. 18.

PINNULARIA SOCIALIS (PALMER)

Valve linear, with rounded ends; axial area broad, one-third the width of the valve; striæ slightly radiate in the middle, convergent at the ends, elsewhere parallel, 8 in 10 µ, crossed by an indistinct band about one-third the length of the striæ. L. 60-120 µ.

This species, discovered by Mr. Palmer near Media, Pa., is remarkable for the grouping of the frustules "held with girdle sides together by a siliceous cementing of valve edges and enclosed in a common coleoderm." The usual number included in a group is four, but sometimes six or eight are noticed. The frustules adhere near their ends and are so firmly fastened that boiling in nitric acid and bichromate of potash for fifteen minutes will not separate them.

_Navicula socialis_ Palmer (Proc. Acad. Nat. Sci., Phila., 1910, p. 460, Pl. 35).

Media, Pa.

Pl. 29, Fig. 5.

{105}PINNULARIA ÆSTUARII CL.

Valve linear, with rounded ends; axial area broad, less than one-third the width of the valve; central area a transverse fascia; striæ, 7 in 10 µ, parallel except at the ends where they are slightly convergent; median line flexuose, with short, terminal semicircular fissures. L. 85 µ.

Port Penn, Delaware River. Rare.

Pl. 29, Fig. 6.

GRACILLIMÆ

PINNULARIA MOLARIS (GRUN.) CL.

Valve very convex, linear, with sub-cuneate ends; axial area narrow, expanded in the middle to a transverse fascia reaching the margin; striæ divergent in the middle, convergent at the ends, 16 in 10 µ. L. 60 µ.

Fresh water.

Pl. 29, Fig. 15.

PINNULARIA LEPTOSOMA GRUN.

Valve linear, rounded at the ends; axial area narrow; central area a broad transverse fascia; striæ slightly divergent in the middle and convergent at the ends, 17 in 10 µ in the middle, closer at the ends. L. 56 µ.

Fresh water. Not common.

Pl. 30, Fig. 10.

CAPITATÆ

PINNULARIA MESOLEPTA EHR.

Valve linear, with triundulate margins and capitate ends; axial area narrow, widened in the middle; striæ divergent in the middle, convergent at the ends, about 12 in 10 µ. L. 34 µ.

Common in fresh water.

Pl. 29, Fig. 13.

PINNULARIA MESOLEPTA VAR. STAURONEIFORMIS GRUN.

Valve triundulate, capitate; axial area narrow, widened in the middle to a transverse fascia, broader at the margin; striæ strongly divergent in the middle and convergent at the ends, 9-10 in 10 µ. L. 70 µ.

Pavonia, N. J., artesian well. Fresh water.

Pl. 30, Fig. 20.

PINNULARIA SUBCAPITATA GREG.

Valve linear or linear-elliptical, with sub-capitate ends; axial area distinct, widened to a transverse fascia in the middle; striæ divergent in the middle, convergent at the ends, 13 in 10 µ. L. 32 µ.

Fresh water.

Pl. 29, Fig. 20.

{106}PINNULARIA SUBCAPITATA VAR. PAUCISTRIATA GRUN.

Valve linear-elliptical, with rounded ends; axial area gradually widened into a broad, transverse fascia; striæ divergent in the middle, convergent at the ends, 11-12 in 10 µ. L. 47 µ.

Fresh water.

Pl. 30, Fig. 16.

PINNULARIA TERMES (EHR.) A. S.

Valve linear, with concave margins and rostrate-capitate ends; axial area narrow, widened in the middle to an orbicular or sub-quadrate space; striæ divergent in the middle, scarcely, if at all, convergent at the ends, 10 in 10 µ.

Pensauken, N. J., artesian well.

Pl. 29, Fig. 17.

This is, I believe, the form figured by Schmidt (Atlas, Pl. 45, Fig. 67). Cleve refers it to Pinnularia interrupta forma biceps, in which the central space is rhomboid.

PINNULARIA TERMES VAR. STAURONEIFORMIS V. H.

Valve linear, with concave margins and capitate-rostrate ends; axial area narrow, widened into a rhomboidal fascia, reaching the margin; striæ, 10 in 10 µ, divergent in the middle, convergent at the ends.

_Pinnularia interrupta forma stauroneiformis_ Cl.

Fresh water.

Pl. 29, Fig. 14.

PINNULARIA APPENDICULATA (AG.) CL.

Valve linear, with subcapitate ends; axial area narrow; central area a transverse fascia; striæ divergent in the middle, convergent at the ends, 16 in 10 µ. L. 43 µ.

Fresh water. Marl pits, Lenola, N. J. (Palmer).

Pl. 29, Fig. 18.

PINNULARIA BRAUNII GRUN.

Valve linear-lanceolate, with capitate ends; axial area gradually widened toward the middle and expanded into a fascia reaching the margin; striæ divergent in the middle, convergent at the ends, 11 in 10 µ. L. 52 µ.

Pensauken, N. J., artesian well.

Pl. 29, Fig. 16.

PINNULARIA MICROSTAURON (EHR.) CL.

Valve convex, linear, tapering to sub-cuneate or sub-rostrate ends; axial area very narrow; central area a broad fascia; striæ divergent in the middle, convergent at the ends, 12 in 10 µ. L. 35 µ.

Pavonia, N. J., artesian well.

Pl. 29, Fig. 19.

This form does not exactly correspond to Cleve's diagnosis, as the ends are not broad. All species in the group Capitatæ are quite variable.

{107}DIVERGENTES

PINNULARIA DIVERGENS VAR. ELLIPTICA GRUN.

Valve linear, with rounded ends; axial area widened in the middle to a transverse fascia; striæ, 9 in 10 µ, divergent in the middle, convergent at the ends. L. 150 µ.

Fresh water. Not common in this locality.

Pl. 31, Fig. 13.

PINNULARIA CARDINALICULUS CL.

Valve linear, with rounded ends; axial area wide, less than one-third the width of the valve, expanded to a transverse fascia; striæ divergent in the middle and slightly convergent at the ends, 9 in 10 µ. L. 97 µ.

Blue clay.

Pl. 30, Fig. 1.

As a rule, the median fissures in Pinnularia are turned inwards on the side of the longer edge of the terminal fissures, but not always. In this specimen the median fissures are turned slightly toward the side of the shorter edge of the terminal fissures.

PINNULARIA LEGUMEN EHR.

Valve linear, with more or less triundulate margins and broad, capitate ends; axial area less than one-fourth the width of valve, widened in the middle; striæ strongly divergent in the middle and convergent at the ends, 10 in 10 µ. L. 84 µ.

Fresh water. May's Landing, N. J.

Pl. 30, Fig. 3.

PINNULARIA LEGUMEN VAR. ?

Valve as in type, but with a transverse fascia; striæ, 10 in 10 µ, curved or bent near the ends. L. 84 µ.

This form is not var. florentina Grun.

May's Landing, N. J. (with the type).

Pl. 30, Fig. 4.

PINNULARIA BRÉBISSONII (KUETZ.) CL.

Valve linear-elliptical, with rounded ends; axial area narrow, widened into a transverse fascia which is usually broader at the ends; striæ divergent in the middle, convergent at the ends, about 12 in 10 µ. L. 40-60 µ (Cl.).

Fresh water. Common.

Pl. 29, Fig. 12; Pl. 31, Fig. 11.

Variable in outline.

PINNULARIA MORMONORUM (GRUN.)

Valve linear, with rounded ends; striæ divergent in the middle, convergent at the ends, 10 in 10 µ; axial area rhombic-lanceolate, widened to a fascia usually reaching the border. L. 62 µ.

_Navicula mormonorum_ Grun.

Common near Willistown, Pa.

This form is regarded by Cleve as P. brébissonii, but the axial area appears to distinguish it. The valves are sometimes narrowed in the middle.

Pl. 29, Fig. 11.

{108}BREVISTRIATÆ

PINNULARIA ACROSPHÆRIA (BRÉB.) CL.

Valve linear, gibbous in the middle and at the ends; axial area about half the width of the valve; median line with approximate central pores; median area punctate; striæ nearly parallel, radiate at the ends, 9 in 10 µ. L. 32-180 µ (Cl.).

Blue clay. Recent, fresh water.

Pl. 30, Fig. 7.

PINNULARIA ACROSPHÆRIA VAR. TURGIDULA GRUN. ?

Valve strongly gibbous in the middle; ends rounded; striæ, 12-13 in 10 µ. L. 54 µ.

Blue clay, Gloucester, N. J., artesian well.

Pl. 30, Fig. 8.

PINNULARIA BLANDITA N. SP.

Valve linear, gibbous in the middle, and with rounded ends; striæ radiate in the middle, convergent at the ends, 13 in 10 µ; axial area about one-fourth the width of the valve, widened in the middle; median line with small semicircular terminal fissures. L. 65 µ.

Pavonia, N. J., artesian well. Rare.

Pl. 30, Fig. 25.

PINNULARIA PARVA (EHR.) CL. VAR. ?

Valve linear, tapering to the subcapitate ends; axial area broad, lanceolate; median line with approximate central pores and semicircular terminal fissures; striæ slightly divergent in the middle and convergent at the ends, 12 in 10 µ. L. 58 µ.

Differs from the type in having finer striæ.

Atco, N. J.

Pl. 30, Fig. 14.

PINNULARIA NODOSA FORMA CAPITATA CL.

Valve triundulate, with capitate ends; axial area about one-fourth the width of valve; striæ parallel, convergent at the ends, 10 in 10 µ, sometimes interrupted in the middle. L. 47 µ.

Fresh water. Common.

Pl. 30, Figs. 15 and 19.

PINNULARIA POLYONCA (BRÉB.) LEWIS

Valve with triundulate margins, more inflated in the middle, with capitate ends; axial area very broad; striæ marginal, short, 9 in 10 µ, divergent in the middle, convergent at the ends. L. 97 µ.

Kirkwood Pond, N. J.

Pl. 30, Fig. 21.

The description of Kuetzing (Species Algarum, p. 85), where he states that the margins are "triundulate, the median inflation larger, apices rounded-capitate," appears to sufficiently distinguish this species, which I believe to be the same as Brun's Navicula peripunctata, except that the form figured (Espèces Nouvelles, Pl. 16, Fig. 11) is interrupted in the middle, a common variation in these forms. Cleve makes Navicula polyonca Bréb. equal Pinnularia mesolepta, but at the same time he considers Lewis' form and also Brun's as equivalent to Navicula formica Ehr., and calls it Pinnularia nodosa var. formica Ehr. P. mesolepta has a narrower area than nodosa. I adhere to Lewis' identification, as in any case it is the form here figured and is nearly, if not quite, the same as Brun's species.

{109}DISTANTES

PINNULARIA LATA (BRÉB.) WM. SM.

Valve linear-elliptical, broad; axial area broad, widened in the middle; striæ slightly radiate in the middle, 3 in 10 µ; median line oblique, the terminal fissures hook-shaped. L. 86 µ.

Blue clay. Not uncommon.

Pl. 30, Fig. 23.

PINNULARIA BOREALIS EHR.

Valve linear, with rounded or sub-truncate ends; axial area about one-fourth the width of the valve, widened in the middle; median line with large hook-shaped terminal fissures; striæ, 4 or 5 in 10 µ. L. 54 µ.

Blue clay. Occasional in fresh water in a smaller form. Specimens occur intermediate between P. lata and P. borealis.

Pl. 30, Fig. 22; Pl. 31, Fig. 12.

PINNULARIA BOREALIS VAR. SCALARIS (EHR.) CL.

Valve narrow, linear; axial area broad, widened into a transverse fascia; striæ, 8 in 10 µ. L. 32 µ.

Fresh water.

Pl. 30, Fig. 24.

TABELLARIÆ

PINNULARIA STOMATOPHORA (GRUN.) CL.

Valve linear, with rounded ends; axial area less than one-third the width of the valve, gradually widened in the middle to a transverse fascia; on each side of the central nodule is a lunate space; striæ divergent in the middle, convergent at the ends, 13 in 10 µ; terminal fissures very long, bayonet shaped. L. 75 µ.

Cleve describes a variety continua as not interrupted. In some forms the fascia is marked by very faint, short striæ on the margin.

Fresh water. Newtown Square.

Pl. 30, Fig. 12.

PINNULARIA GIBBA (KUETZ.) V. H.

Valve linear, tapering to the subcapitate ends; axial area dilated in the middle; striæ, 10-11 µ, divergent in the middle, convergent at the ends. L. 80 µ.

Fresh water.

Pl. 30, Fig. 5.

PINNULARIA MESOGONGYLA (EHR.) CL.

Valve linear, gibbous in the middle, ends subcapitate; axial area narrow, widened in the middle to a large orbicular space; striæ strongly divergent in the middle, convergent at the ends, 11 in 10 µ. L. 60 µ.

Fresh water. Common.

Pl. 30, Fig. 6.

{110}PINNULARIA STAUROPTERA (GRUN.) CL.

Valve linear, with slightly triundulate margins tapering to the subcapitate ends; axial area more than one-third the width of the valve, slightly widened in the middle; median line with approximate central pores and semicircular terminal fissures; striæ divergent in the middle, convergent at the ends, 11 in 10 µ. L. 82 µ.

May's Landing, N. J.

Pl. 30, Fig. 13.

Some of the forms are more triundulate than the specimen figured.

PINNULARIA STAUROPTERA VAR. INTERRUPTA CL.

Valve linear, tapering to the subcapitate ends; axial area broad, widened in the middle to a transverse fascia; striæ divergent in the middle, convergent at the ends, 10 in 10 µ; median pores approximate. L. 118 µ.

Schuylkill River.

Pl. 30, Fig. 11.

PINNULARIA TABELLARIA (EHR.) CL.

Valve linear, gibbous in the middle and tapering to the subcapitate ends; axial area about one-third the width of the valve, widened in the middle; median line with approximate central pores and bayonet-shaped terminal fissures; striæ sometimes unilaterally interrupted, divergent in the middle, strongly convergent at the ends, 9 in 10 µ. L. 138 µ.

Blue clay. Rare.

Pl. 30, Fig. 9.

The form here figured has coarser striæ than in the type which is also usually more capitate.

P. legumen has triundulate margins, P. mesogongyla has an orbicular space, while P. gibba has the space widened. According to Cleve, P. gibba has approximate central pores, as has also P. mesogongyla. In what I have considered to be P. legumen, the central pores are more approximate than in the other two species mentioned. In fact, all of the three resemble each other closely, and are variously named by different authors. The form of P. gibba here figured, which may be P. stauroptera, is not the typical form of Wm. Smith, which has a narrow area and central space. There are, however, among the typical specimens in H. L. Smith's Type Slide No. 275, smaller valves which show a resemblance.

MARINÆ

PINNULARIA RECTANGULATA (GREG.) CL.

Valve linear, with abruptly rounded ends; axial area very narrow; central area large, somewhat quadrate; striæ, 7-8 in 10 µ. L. 78 µ.

_Navicula rectangulata Greg._

Shark River, N. J.

Pl. 29, Fig. 7.

{111}EPITHEMIA BRÉB. (1838)

(epithema, a cover or lid)

Frustules epiphytic, solitary, sometimes geminate, adherent on the ventral side at the ends; in zone view rectangular, sometimes tumid in the middle. Valve arcuate, having an interior costate stratum or transverse septa extending to the girdle, often detached, and an exterior valve surface with transverse rows of puncta. Central and terminal nodules not easily seen; in some species a true raphe is indicated.

The resemblance between Epithemia and Eunotia has been already mentioned. In the shape and striation of the valves there is an approach to Cymbella.

The genus is divided into two groups, one in which the costæ alternate with double rows of puncta, as in E. turgida, and the other in which the rows of puncta are more than two.

The endochrome usually consists of a band lying along the ventral zone and extending in two flaps on the valves.

EPITHEMIA TURGIDA (EHR.) KUETZ.

Valve arcuate, with ends subcapitate; costæ radiate, 4 in 10 µ, alternating with double rows of puncta. Median nodule central, the raphe curved toward the ventral edge which it closely follows.

Parasitic on algæ. Very common in fresh water, especially in ponds. In the figure the valve is asymmetrical with respect to the transverse axis, an unusual condition.

Pl. 31, Fig. 14.

EPITHEMIA ARGUS KUETZ.

Valve with dorsal margin convex, and ventral margin nearly straight; ends rounded, constricted; costæ robust, alternating with more than two rows of puncta; zone view rectangular, the thickened ends of the costæ forming large nodules in a row along the edge of the valve next to the connecting zone.

_Cystopleura argus_ (Ehr.) Kunze.

Common in fresh water.

Pl. 31, Figs. 15 and 21.

EPITHEMIA ARGUS VAR. ?

Valve strongly arcuate on the dorsal side and concave on the ventral; tapering to the rounded but not produced ends; costæ at unequal distances, about 2 in 10 µ; granules in transverse rows, 8 in 10 µ. L. 100 µ.

Pensauken, N. J., artesian well.

Pl. 31, Fig. 16.

EPITHEMIA MUELLERI A. S. ?

Valve broad, convex, slightly arcuate, with obtuse, somewhat constricted apices; costæ about 4 in 10 µ; striæ, 12-14 in 10 µ; in zone view the outline is rectangular, slightly tumid in the middle. L. 78 µ.

Blue clay.

Pl. 31, Fig. 17.

{112}EPITHEMIA ZEBRA VAR. PROBOSCIDEA (KUETZ.) GRUN.

Valve convex on the dorsal, concave on the ventral side; costæ, 3-4 in 10 µ, slightly radiating; apices recurved, capitate.

Blue clay.

Pl. 31, Fig. 18.

EPITHEMIA GIBBERULA VAR. PRODUCTA GRUN.

Valve narrow, lunate, with produced and arcuate apices; costæ radiate, 3-4 in 10 µ; striæ, 16-18 in 10 µ, punctate. L. 58 µ, usually smaller.

Blue clay.

Pl. 31, Fig. 19.

EPITHEMIA MUSCULUS KUETZ.