CHAPTER X

THE SCYPHOPHORI, HAPLOMI, AND XENOMI

=ORDER Scyphophori.=—The _Scyphophori_ (σκύφος, cup; φορέω, to bear) constitutes a small order which lies apparently between the _Gymnonoti_ and the _Isospondyli_. Boulenger unites it with the _Isospondyli_. The species, about seventy-five in number, inhabit the rivers of Africa, where they are important as food-fishes. In all there is a deep cavity on each side of the cranium covered by a thin bony plate, the supertemporal bone. There is no symplectic bone, and the subopercle is very small or concealed. The gill-openings are narrow and there are no pharyngeal teeth. The air-bladder connects with the ear, but not apparently in the same way as with the _Ostariophysan_ fishes, to which, however, the _Scyphophori_ are most nearly related. In all the _Scyphophori_ the body is oblong, covered with cycloid scales, the head is naked, there are no barbels, and the small mouth is at the end of a long snout. All the species possess a peculiar organ on the tail, which with reference to a similar structure in _Torpedo_ and _Electrophorus_ is held to be a degenerate electric organ. According to Günther, "it is without electric functions, but evidently representing a transitional condition from muscular substance to an electric organ. It is an oblong capsule divided into numerous compartments by vertical transverse septa and containing a gelatinous substance."

=The Mormyridæ.=—There are two families of _Scyphophori_. The _Mormyridæ_ have the ordinary fins and tail of fishes and the _Gymnarchidæ_ are eel-like, with ventrals, anal and caudal wanting. _Gymnarchus miloticus_ of the Nile reaches a length of six feet, and it is remarkable as retaining the cellular structure of the air-bladder as seen in the garpike and bowfin. It doubtless serves as an imperfect lung.

The best-known genus of _Scyphophori_ is _Mormyrus_. Species of this genus found in the Nile were worshiped as sacred by the ancient Egyptians and pictures of _Mormyrus_ are often seen among the emblematic inscriptions. The Egyptians did not eat the _Mormyrus_ because with two other fishes it was accused of having devoured a limb from the body of Osiris, so that Isis was unable to recover it when she gathered the scattered remains of her husband.

In _Mormyrus_ the bones of the head are covered by skin, the snout is more or less elongated, and the tail is generally short and insignificant. One of the most characteristically eccentric species is _Gnathonemus curvirostris_, lately discovered by Dr. Boulenger from the Congo. Fossil _Mormyridæ_ are unknown.

=The Haplomi.=—In the groups called _Iniomi_ and _Lyopomi_, the mesocoracoid arch is imperfect or wanting, a condition which in some cases may be due to the degeneration produced by deep-sea life. In the eels a similar condition obtains. In the group called _Haplomi_ (ἁπλοός, simple; ὤμος, shoulder), as in all the groups of fishes yet to be discussed, this arch is wholly wanting at all stages of development. In common with the _Isospondyli_ and with soft-rayed fishes in general the air-bladder has a persistent air-duct, all the fins are without true spines, the ventral fins are abdominal, and the scales are cycloid. The group is a transitional one, lying almost equidistant between the _Isospondyli_ and the _Acanthopterygii_. Gill unites it with the latter and Woodward with the former. We may regard it for the present as a distinct order, although no character of high importance separates it from either. Hay unites the _Haplom_i with the _Synentognathi_ to form the order of _Mesichthyes_, or transitional fishes, but the affinities of either with other groups are quite as well marked as their relation to each other. Boulenger unites the _Iniomi_ with the _Haplomi_, an arrangement which apparently has merit, for the most primitive and non-degenerate _Iniomi_, as _Aulopus_ and _Synodus_, lack both mesocoracoid and orbitosphenoid. These bones are characteristic of the _Isospondyli_, but are wanting in _Haplomi_.

There is no adipose dorsal in the typical _Haplomi_, the dorsal is inserted far back, and the head is generally scaly. Most but not all of the species are of small size, living in fresh or brackish water, and they are found in almost all warm regions, though scantily represented in California, Japan, and Polynesia. The four families of typical _Haplomi_ differ considerably from one another and are easily distinguished, although obviously related. Several other families are provisionally added to this group on account of agreement in technical characters, but their actual relationships are uncertain.

=The Pikes.=—The _Esocidæ_ have the body long and slender and the mouth large, its bones armed with very strong, sharp teeth of different sizes, some of them being movable. The upper jaw is not projectile, and its margin, as in the _Salmonidæ_, is formed by the maxillary. The scales are small, and the dorsal fin far back and opposite the anal, and the stomach is without pyloric cæca. There is but a single genus, _Esox_ (_Lucius_ of Rafinesque), with about five or six living species. Four of these are North American, the other one being found in Europe, Asia, and North America.

All the pikes are greedy and voracious fishes, very destructive to other species which may happen to be their neighbors; "mere machines for the assimilation of other organisms." Thoreau describes the pike as "the swiftest, wariest, and most ravenous of fishes, which Josselyn calls the river-wolf. It is a solemn, stately, ruminant fish, lurking under the shadow of a lily-pad at noon, with still, circumspect, voracious eye; motionless as a jewel set in water, or moving slowly along to take up its position; darting from time to time at such unlucky fish or frog or insect as comes within its range, and swallowing it at one gulp. Sometimes a striped snake, bound for greener meadows across the stream, ends its undulatory progress in the same receptacle."

As food-fishes, all the _Esocidæ_ rank high. Their flesh is white, fine-grained, disposed in flakes, and of excellent flavor.

The finest of the _Esocidæ_, a species to be compared, as a grand game fish, with the salmon, is the muskallunge (_Esox masquinongy_). Technically this species may be known by the fact that its cheeks and opercles are both naked on the lower half. It may be known also by its great size and by its color, young and old being spotted with black on a golden-olive ground.

The muskallunge is found only in the Great Lake region, where it inhabits the deeper waters, except for a short time in the spring, when it enters the streams to spawn. It often reaches a length of six feet and a weight of sixty to eighty pounds. It is necessarily somewhat rare, for no small locality would furnish food for more than one such giant. It is, says Hallock, "a long, slim, strong, and swift fish, in every way formed for the life it leads, that of a dauntless marauder."

A second species of muskallunge, _Esox ohiensis_, unspotted but vaguely cross-barred, occurs sparingly in the Ohio River and the upper Mississippi Valley. It is especially abundant in Chautauqua Lake.

The pike (_Esox lucius_) is smaller than the muskallunge, and is technically best distinguished by the fact that the opercles are naked below, while the cheeks are entirely scaly. The spots and cross-bars in the pike are whitish or yellowish, and always paler than the olive-gray ground color. It is the most widely distributed of all fresh-water fishes, being found from the upper Mississippi Valley, the Great Lakes, and New England to Alaska and throughout northern Asia and Europe. It reaches a weight of ten to twenty pounds or more, being a large strong fish in its way, inferior only to the muskallunge. In England _Esox lucius_ is known as the pike, while its young are called by the diminutive term pickerel. In America the name pickerel is usually given to the smaller species, and sometimes even to _Esox lucius_ itself, the word being with us a synonym for pike, not a diminutive.

Of the small pike or pickerel we have three species in the eastern United States. They are greenish in color and banded or reticulated, rather than spotted, and, in all, the opercles as well as the cheeks are fully covered with scales. One of these (_Esox reticulatus_) is the common pickerel of the Eastern States, which reaches a respectable size and is excellent as food. The others, _Esox americanus_ along the Atlantic seaboard and _Esox vermiculatus_ in the middle West, seldom exceed a foot in length and are of no economic importance.

Numerous fossil species are found in the Tertiary of Europe, _Esox lepidotus_ from the Miocene of Baden being one of the earliest and the best known; in this species the scales are much larger than in the recent species. The fossil remains would seem to indicate that the origin of the family was in southern Europe, although most of the living species are American.

=The Mud-minnows.=—Close to the pike is the family of _Umbridæ_, or mud-minnows, which technically differ from the pikes only in the short snout, small mouth, and weak dentition. The mud-minnows are small, sluggish, carnivorous fishes living in the mud at the bottom of cold, clear streams and ponds. They are extremely tenacious of life, though soon suffocated in warm waters. The barred mud-minnow of the prairies of the middle West (_Umbra limi_) often remains in dried sloughs and bog-holes, and has been sometimes plowed up alive. _Umbra pygmæa_, a striped species, is found in the Eastern States and _Umbra crameri_ in bogs and brooks along the Danube. This wide break in distribution seems to indicate a former wide extension of the range of _Umbridæ_, perhaps coextensive with _Esox_. Fossil _Umbridæ_ are, however, not yet recognized.

=The Killifishes.=—Most of the recent _Haplomi_ belong to the family of _Pœciliidæ_ (killifishes, or Cyprinodonts). In this group the small mouth is extremely protractile, its margin formed by the premaxillaries alone much as in the spiny-rayed fishes. The teeth are small and of various forms according to the food. In most of the herbivorous forms they are incisor-like, serrate, and loosely inserted in the lips. In the species that eat insects or worms they are more firmly fixed. The head is scaly, the stomach without cæca, and the intestines are long in the plant-eating species and short in the others. There are nearly 200 species, very abundant from New England and California southward to Argentina, and in Asia and Africa also. In regions where rice is produced, they swarm in the rice swamps and ditches. Some of them enter the sea, but none of them go far from shore. Some are brilliantly colored, and in many species the males are quite unlike the females, being smaller and more showy. The largest species (_Fundulus_, _Anableps_) rarely reach the length of a foot, while _Heterandria formosa_, a diminutive inhabitant of the Florida rivers, scarcely reaches an inch. Some species are oviparous, but in most of the herbivorous forms, and some of the others, the eggs are hatched within the body, and the anal in the male is modified into a long sword-shaped intromittent organ, placed farther forward than the anal in the female. The young when born closely resemble the parent. Most of the insectivorous species swim at the surface, moving slowly with the eyes partly out of water. This habit in the genus _Anableps_ (four-eyed fish, or _Cuatro ojos_) is associated with an extraordinary structure of the eye. This organ is prominent and is divided by a horizontal partition into two parts, the upper, less convex, adopted for sight in the air, the lower in the water. The few species of _Anableps_ are found in tropical America. The species of some genera swim near the bottom, but always in very shallow waters. All are very tenacious of life, and none have any commercial value although the flesh is good.

The unique structure of the eye of this curious fish has been carefully studied by Mr. M. C. Marsh, pathologist of the U. S. Fish Commission, who furnishes the following notes published by Evermann & Goldsborough:

"The eye is crossed by a bar, like the diameter of a circle, and parallel with the length of the body. This bar is darker than the other external portions of the eyeball and has its edges darker still. Dividing the external aspect of the eye equally, it has its lower edge on the same level as the back of the fish, which is flat and straight from snout to dorsal, or nearly the whole length of the fish; so that when the body of the fish is just submerged the level of the water reaches to this bar, and the lower half of the eye is in water, the upper half in the air. Upon dissecting the eyeball from the orbit, it appears nearly round. A membranous sheath covers the external part and invests most of the ball. It may be peeled off, when the dark bar on the external portion of the eye is seen to be upon this membrane, which may correspond to the conjunctiva. The back portion of the eyeball being cut off, one lens is found. The lining of the ball consists, in front, of one black layer, evidently choroid. Behind there is a retinal layer. The choroid layer turns up anteriorly, making a free edge comparable to an iris. The free edge is chiefly evident in the lower part of the eye. A large pupil is left, but is divided by two flaps, continuations of the choroid coat, projecting from either side and overlapping. There are properly then two pupils, an upper and lower, separated by a band consisting of the two flaps, which may probably, by moving upward and downward, increase or diminish the size of either pupil; an upward motion of the flaps increasing the lower pupil at the expense of the other, and vice versa."

This division of the pupil into two parts permits the fish, when swimming at the surface of the water, as is its usual custom, to see in the air with the upper portion and in the water with the lower. It is thus able to see not only such insects as are upon the surface of the water or flying in the air above, but also any that may be swimming beneath the surface.

According to Mr. E. W. Nelson, "the individuals of this species swim always at the surface and in little schools arranged in platoons or abreast. They always swim headed upstream against the current, and feed upon floating matter which the current brings them. A platoon may be seen in regular formation breasting the current, either making slight headway upstream or merely maintaining their station, and on the qui vive for any suitable food the current may bring. Now and then one may be seen to dart forward, seize a floating food particle, and then resume its place in the platoon. And thus they may be observed feeding for long periods. They are almost invariably found in running water well out in the stream, or at least where the current is strongest and where floating matter is most abundant, for it is upon floating matter that they seem chiefly to depend. They are not known to jump out of the water to catch insects flying in the air or resting upon vegetation above the water surface, nor do they seem to feed to any extent upon all small crustaceans or other portions of the plankton beneath the surface.

"When alarmed—and they are wary and very easily frightened—they escape by skipping or jumping over the water, 2 or 3 feet at a skip. They rise entirely out of the water, and at a considerable angle, the head pointing upward. In descending the tail strikes the water first and apparently by a sculling motion new impetus is acquired for another leap. This skipping may continue until the school is widely scattered. When a school has become scattered, and after the cause of their fright has disappeared, the individuals soon rejoin each other. First two will join each other and one by one the others will join them until the whole school is together again. Rarely do they attempt to dive or get beneath the surface; when they do they have great difficulty in keeping under and soon come to the surface again."

Of the many genera of _Pœciliidæ_, top-minnows, and killifishes we may mention the following: _Cyprinodon_ is made up of chubby little fishes of eastern America with tricuspid, incisor teeth, oviparous and omnivorous. Very similar to these but smaller are the species of _Lebias_ in southern Europe. _Jordanella floridæ_ of the Florida everglades is similar, but with the dorsal fin long and its first ray enlarged and spine-like. It strongly resembles a young sunfish. Most of the larger forms belong to _Fundulus_, a genus widely distributed from Maine to Guatemala and north to Kansas and southern California. _Fundulus majalis_, the Mayfish of the Atlantic Coast, is the largest of the genus. _Fundulus heteroclitus_, the killifish, the most abundant. _Fundulus diaphanus_ inhabits sea and lake indiscriminately. _Fundulus stellifer_ of the Alabama is beautifully colored, as is _Fundulus zebrinus_ of the Rio Grande. The genus _Zygonectes_ includes dwarf species similar to _Fundulus_, and _Adinia_ includes those with short, deep body. _Goodea atripinnis_ with tricuspid teeth lives in warm springs in Mexico, and several species of _Goodea_, _Gambusia_, _Pœcilia_, and other genera inhabit hot springs of Mexico, Central America, and Africa. The genus _Gambusia_, the top-minnows, includes numerous species with dwarf males having the anal modified. _Gambusia affinis_ abounds in all kinds of sluggish water in the southern lowlands, gutters and even sewers included. It brings forth its brood in early spring. Viviparous and herbivorous with modified anal fin are the species of _Pœcilia_, abundant throughout Mexico and southward to Brazil; _Mollienesia_ very similar, with a banner-like dorsal fin, showily marked, occurs from Louisiana southward, and _Xiphophorus_, with a sword-shaped lobe on the caudal, abounds in Mexico; _Characodon_ and _Goodea_ (see Fig. 53, Vol. I) in Mexico have notched teeth, and finally, _Heterandria_ contains some of the least of fishes, the handsomely colored males barely half an inch long.

In Lake Titicaca in the high Andes is a peculiar genus (_Orestias_) without ventral fins. Still more peculiar is _Empetrichthys merriami_ of the desert springs of the hot and rainless Death Valley in California, similar to _Orestias_, but with enormously enlarged pharyngeals and pharyngeal teeth, an adaptation to some unknown purpose. Fossil Cyprinodonts are not rare from the Miocene in southern Europe. The numerous species are allied to _Lebias_ and _Cyprinodon_, and are referred to _Prolebias_ and _Pachylebias_. None are American, although two American extinct genera, _Gephyrura_ and _Proballostomus_, are probably allied to this group.

=Amblyopsidæ.=—The cavefishes, _Amblyopsidæ_, are the most remarkable of the haplomous fishes. In this family the vent is placed at the throat. The form is that of the _Pœciliidæ_, but the mouth is larger and not protractile. The species are viviparous, the young being born at about the length of a quarter of an inch.

In the primitive genus _Chologaster_, the fish of the Dismal Swamp, the eyes are small but normally developed. _Chologaster cornutus_ abounds in the black waters of the Dismal Swamp of Virginia, thence southward through swamps and rice-fields to Okefinokee Swamp in northern Florida. It is a small fish, less than two inches long, striped with black, and with the habit of a top-minnow. Other species of _Chologaster_, possessing eyes and color, but provided also with tactile papillæ, are found in cave springs in Tennessee and southern Illinois.

From _Chologaster_ is directly descended the small blindfish _Typhlichthys subterraneus_ of the caves of the Subcarboniferous limestone rocks of southern Indiana and southward to northern Alabama. As in _Chologaster_, the ventral fins are wanting. The eyes, present in the young, become defective and useless in the adult, when they are almost hidden by other tissues. The different parts of the eye are all more or less incomplete, being without function. The structure of the eye has been described in much detail in several papers by Dr. Carl H. Eigenmann. As to the cause of the loss of eyesight two chief theories exist—the Lamarckian theory of the inheritance in the species of the results of disuse in the individual and the Weissmannian doctrine that the loss of sight is a result of panmixia or cessation of selection. This may be extended to cover reversal of selection, as in the depths of the great caves the fish without eyes would be at some slight advantage. Dr. Eigenmann inclines to the Lamarckian doctrine, but the evidence brought forward fails to convince the present writer that results of individual use or disuse ever become hereditary or that they are ever incorporated in the characters of a species. In the caves of southern Missouri is an independent case of similar degradation. _Troglichthys rosæ_, the blindfish of this region, has the eye in a different phase of degeneration. It is thought to be separately descended from some other species of _Chologaster_. Of this species Mr. Garman and Mr. Eigenmann have given detailed accounts from somewhat different points of view.

Concerning the habits of the blindfish (_Troglichthys rosæ_), Mr. Garman quotes the following from notes of Miss Ruth Hoppin, of Jasper County, Missouri: "For about two weeks I have been watching a fish taken from a well. I gave him considerable water, changed once a day, and kept him in an uninhabited place subject to as few changes of temperature as possible. He seems perfectly healthy and as lively as when first taken from the well. If not capable of long fasts, he must live on small organisms my eye cannot discern. He is hardly ever still, but moves about the sides of the vessel constantly, down and up, as if needing the air. He never swims through the body of the water away from the sides unless disturbed. Passing the finger over the sides of the vessel under water I find it slippery. I am careful not to disturb this slimy coating when the water is changed.... Numerous tests convince me that it is through the sense of touch, and not through hearing, that the fish is disturbed; I may scream or strike metal bodies together over him as near as possible, yet he seems to take no notice whatever. If I strike the vessel so that the water is set in motion, he darts away from that side through the mass of water, instead of around in his usual way. If I stir the water or touch the fish, no matter how lightly, his actions are the same."

The more famous blindfish of the Mammoth Cave, _Amblyopsis spelæus_, reaches a length of five inches. It possesses ventral fins. From this fact we may infer its descent from some extinct genus which, unlike _Chologaster_, retains these fins. The translucent body, as in the other blindfishes, is covered with very delicate tactile papillæ, which form a very delicate organ of touch.

The anomalous position of the vent in _Amblyopsidæ_ occurs again in an equally singular fish, _Aphredoderus sayanus_, which is found in the same waters throughout the same region in which _Chologaster_ occurs. It would seem as if these lowland fishes of the southern swamps were remains of a once much more extensive fauna.

No fossil allies of _Chologaster_ are known.

=Kneriidæ, etc.=—The members of the order of _Haplomi_, recorded above, differ widely among themselves in various details of osteology. There are other families, probably belonging here, which are still more aberrant. Among these are the _Kneriidæ_, and perhaps the entire series of forms called _Iniomi_, most of which possess the osteological traits of the _Haplomi_.

The family of _Kneriidæ_ includes a few very small fishes of the rivers of Africa.

=The Galaxiidæ.=—The _Galaxiidæ_ are trout-like fishes of the southern rivers, where they take the place of the trout of the northern zones. The species lack the adipose fins and have the dorsal inserted well backward. According to Boulenger these fishes, having no mesocoraoid, should be placed among the _Haplomi_. Yet their relation to the _Haplochitonidæ_ is very close and both families may really belong to the _Isospondyli_. _Galaxias truttaceus_ is the kokopu, or "trout," of New Zealand. _Galaxias ocellatus_ is the yarra trout of Australia. Several other species are found in southern Australia, Tasmania, Patagonia, and the Falkland Islands, and even in South Africa. This very wide distribution in the rivers remote from each other has given rise to the suggestion of a former land connection between Australia and Patagonia. Other similar facts have led some geologists to believe in the existence of a former great continent called Antarctica, now submerged except that part which constitutes the present unknown land of the Antarctic.

As intimated on p. 253, Vol. I, this distribution of _Galaxias_ with similar anomalies in other groups could not if unsupported by geological evidence be held to prove the former extension of the Antarctic continent. Dr. Boulenger[12] has recently shown that _Galaxias_ lives freely in salt water, a fact sufficient to account for its wide distribution in the rivers of the southern hemisphere.

Footnote 12:

Dr. Boulenger (_Nature_, Nov. 27, 1902) has the following note on _Galaxias_: "Most text-books and papers discussing geographical distribution have made much of the range of a genus of small fishes, somewhat resembling trout, the _Galaxias_, commonly described as true fresh-water forms, which have long been known from the extreme south of South America, New Zealand, Tasmania, and southern Australia. The discovery, within the last few years, of a species of the same genus in fresh water near Cape Town, whence it had previously been described as a loach by F. de Castelnau, has added to the interest, and has been adduced as a further argument in support of the former existence of an Antarctic continent. In alluding to this discovery when discussing the distribution of African fresh-water fishes in the introduction to my work 'Les Poissons du Bassin du Congo,' in 1901, I observed that, contrary to the prevailing notion, all species of _Galaxias_ are not confined to fresh water, and that the fact of some living both in the sea and in rivers suffices to explain the curious distribution of the genus; pointing out that in all probability these fishes were formerly more widely distributed in the seas south of the tropic of Capricorn, and that certain species, adapting themselves entirely to fresh-water life, have become localized at the distant points where they are now known to exist. Although as recently as October last the distinguished American ichthyologist D. S. Jordan wrote (_Science_, xiv, p. 20): 'We know nothing of the power of _Galaxias_ to survive submergence in salt water, if carried in a marine current': it is an established fact, ascertained some years ago by F. E. Clarke in New Zealand and by R. Vallentin in the Falkland Islands, that _Galaxias attenuatus_ lives also in the sea. In New Zealand it periodically descends to the sea, where it spawns, from January to March, and returns from March to May. In accordance with these marine habits, this species has a much wider range than any of the others, being known from Chile, Patagonia, Tierra del Fuego, the Falkland Islands, New Zealand, Tasmania, and southern Australia.

"I now wish to draw attention to a communication made by Captain F. W. Hutton in the last number of the Transactions of the New Zealand Institute (xxxiv, p. 198), 'On a Marine Galaxias from the Auckland Islands.' This fish, named _Galaxias bollansi_, was taken out of the mouth of a specimen of _Merganser australis_ during the collection excursion to the southern islands of New Zealand made in January, 1901, by His Excellency the Earl of Ranfurly.

"It is hoped that by giving greater publicity to these discoveries the family _Galaxiidæ_ will no longer be included among those strictly confined to fresh waters, and that students of the geographical distribution of animals will be furnished with a clue to a problem that has so often been discussed on insufficient data. As observed by Jordan (_l. c._), all anomalies in distribution cease to be such when the facts necessary to understand them are at hand.'

"Of the fresh-water species of _Galaxias_, eight are known from New Zealand and the neighboring islands, seven from New South Wales, three or four from south Australia, one from west Australia, two from Tasmania, seven from South America, from Chile southwards, and one from the Cape of Good Hope."

_Neochanna_ is an ally of _Galaxias_ living in burrows in the clay or mud like a crayfish, often at a distance from water. As in various other mud-living types, the ventral fins are obsolete.

=Order Xenomi.=—We must place near the _Haplomi_ the singular group of _Xenomi_ (ξενός, strange; ὤμος, shoulder), regarded by Dr. Gill as a distinct order. Externally these fish much resemble the mud-minnows, differing mainly in the very broad pectorals. But the skeleton is thin and papery, the two coracoids forming a single cartilaginous plate imperfectly divided. The pectorals are attached directly to this without the intervention of actinosts, but in the distal third, according to Dr. Charles H. Gilbert, the coracoid plate begins to break up into a fringe of narrow cartilaginous strips. These about equal the very large number (33 to 36) of pectoral rays, the basal part of each ray being slightly forked to receive the tip of the cartilaginous strip.

"In the deep-sea eels of the order _Heteromi_ there is a somewhat similar condition of the coracoid elements inasmuch as the hypercoracoid and hypocoracoid though present are merely membranous elements surrounded by cartilage and the actinosts are greatly reduced. It seems probable that we are dealing in the two cases with independent degeneration of the shoulder-girdle and that the two groups (_Xenomi_ and _Heteromi_) are not really related." (Gilbert.)

Of the single family _Dalliidæ_, one species is known, the Alaska blackfish, _Dallia pectoralis_.

This animal, formed like a mud-minnow, reaches a length of eight inches and swarms in the bogs and sphagnum swamps of northwestern Alaska and westward through Siberia. It is found in countless numbers according to its discoverer, Mr. L. M. Turner, "wherever there is water enough to wet the skin of a fish," and wherever it occurs it forms the chief food of the natives. Its vitality is most extraordinary. Blackfishes will remain frozen in baskets for weeks and when thawed out are as lively as ever. Turner gives an account of a frozen individual swallowed by a dog which escaped in safety after being thawed out by the heat of the dog's stomach.