The Grayling, or Thymallidæ.—The small family of Thymallidæ, or grayling, is composed of finely organized fishes allied to the trout, but differing in having the frontal bones meeting on the middle line of the skull, thus excluding the frontals from contact with the supraoccipital. The anterior half of the very high dorsal is made up of unbranched simple rays. There is but one genus, Thymallus, comprising very noble game-fishes characteristic of subarctic streams.

The grayling, Thymallus, of Europe, is termed by Saint Ambrose "the flower of fishes." The teeth on the tongue, found in all the trout and salmon, are obsolete in the grayling. The chief distinctive peculiarity of the genus Thymallus is the great development of the dorsal fin, which has more rays (20 to 24) than are found in any of the Salmonidæ, and the fin is also higher. All the species are gaily colored, the dorsal fin especially being marked with purplish or greenish bands and bright rose-colored spots; while the body is mostly purplish gray, often with spots of black. Most of the species rarely exceed a foot in length, but northward they grow larger. Grayling weighing five pounds have been taken in England; and according to Dr. Day they are said in Lapland to reach a weight of eight or nine pounds. The grayling in all countries frequent clear, cold brooks, and rarely, if ever, enter the sea, or even the larger lakes. They congregate in small shoals in the streams, and prefer those which have a succession of pools and shallows, with a sandy or gravelly rather than rocky bottom. The grayling spawns on the shallows in April or May (in England). It is non-migratory in its habits, depositing its ova in the neighborhood of its usual haunts. The ova are far more delicate and easily killed than those of the trout or charr. The grayling and the trout often inhabit the same waters, but not altogether in harmony. It is said that the grayling devours the eggs of the trout. It is certain that the trout feed on the young grayling. As a food-fish, the grayling of course ranks high; and it is beloved by the sportsman. They are considered gamy fishes, although less strong than the brook-trout, and perhaps less wary. The five or six known species of grayling are very closely related, and are doubtless comparatively recent offshoots from a common stock, which has now spread itself widely through the northern regions.

The common grayling of Europe (Thymallus thymallus) is found throughout northern Europe, and as far south as the mountains of Hungary and northern Italy. The name Thymallus was given by the ancients, because the fish, when fresh, was said to have the odor of water-thyme. Grayling belonging to this or other species are found in the waters of Russia and Siberia.

The American grayling (Thymallus signifer) is widely distributed in British America and Alaska. In the Yukon it is very abundant, rising readily to the fly. In several streams in northern Michigan, Au Sable River, and Jordan River in the southern peninsula, and Otter Creek near Keweenaw in the northern peninsula, occurs a dwarfish variety or species with shorter and lower dorsal fins, known to anglers as the Michigan grayling (Thymallus tricolor). This form has a longer head, rather smaller scales, and the dorsal fin rather lower than in the northern form (signifer); but the constancy of these characters in specimens from intermediate localities is yet to be proved. Another very similar form, called Thymallus montanus, occurs in the Gallatin, Madison, and other rivers of Western Montana tributary to the Missouri. It is locally still abundant and one of the finest of game-fishes. It is probable that the grayling once had a wider range to the southward than now, and that so far as the waters of the United States are concerned it is tending toward extinction. This tendency is, of course, being accelerated in Michigan by lumbermen and anglers. The colonies of grayling in Michigan and Montana are probably remains of a post-glacial fauna.

The Argentinidæ.—The family of Argentinidæ, or smelt, is very closely related to the Salmonidæ, representing a dwarf series of similar type. The chief essential difference lies in the form of the stomach, which is a blind sac, the two openings near together, and about the second or pyloric opening there are few if any pyloric cæca. In all the Salmonidæ the stomach has the form of a siphon, and about the pylorus there are very many pyloric cæca. The smelt have the adipose fin and the general structure of the salmon. All the species are small in size, and most of them are strictly marine, though some of them ascend the rivers to spawn, just as salmon do, but not going very far. A few kinds become landlocked in ponds. Most of the species are confined to the north temperate zone, and a few sink into the deep seas. All that are sufficiently abundant furnish excellent food, the flesh being extremely delicate and often charged with a fragrant oil easy of digestion.

The best-known genus, Osmerus, includes the smelt, or spirling (éperlan), of Europe, and its relatives, all excellent food-fishes, although quickly spoiling in warm weather. Osmerus eperlanus is the European species; Osmerus mordax of our eastern coast is very much like it, as is also the rainbow-smelt, Osmerus dentex of Japan and Alaska. A larger smelt, Osmerus albatrossis, occurs on the coast of Alaska, and a small and feeble one, Osmerus thaleichthys, mixed with other small or delicate fishes, is the whitebait of the San Francisco restaurants. The whitebait of the London epicure is made up of the young of herrings and sprats of different species. The still more delicate whitebait of the Hong Kong hotels is the icefish, Salanx chinensis. Retropinna retropinna, so called from the backward insertion of its dorsal, is the excellent smelt of the rivers of New Zealand. All the other species belong to northern waters. Mesopus, the surf-smelt, has a smaller mouth than Osmerus and inhabits the North Pacific. The California species, Mesopus pretiosus, of Neah Bay has, according to James G. Swan, "the belly covered with a coating of yellow fat which imparts an oily appearance to the water where the fish has been cleansed or washed and makes them the very perfection of pan-fish." This species spawns in late summer along the surf-line. According to Mr. Swan the water seems to be filled with them. "They come in with the flood-tide, and when a wave breaks upon the beach they crowd up into the very foam, and as the surf recedes many will be seen flapping on the sand and shingle, but invariably returning with the undertow to deeper water." The Quilliute Indians of Washington believe that "the first surf-smelts that appear must not be sold or given away to be taken to another place, nor must they be cut transversely, but split open with a mussel-shell."

The surf-smelt is marine, as is also a similar species, Mesopus japonicus, in Japan. Mesopus olidus, the pond-smelt of Alaska, Kamchatka, and Northern Japan, spawns in fresh-water ponds.

Still more excellent as a food-fish than even these exquisite species is the famous eulachon, or candle-fish (Thaleichthys pacificus). The Chinook name, usually written eulachon, is perhaps more accurately represented as ulchen. This little fish has the form of a smelt and reaches the length of nearly a foot. In the spring it ascends in enormous numbers all the rivers north of the Columbia, as far as Skaguay, for a short distance for the purpose of spawning. These runs take place usually in advance of the salmon-runs. Various predatory fishes and sea-birds persecute the eulachon during its runs, and even the stomachs of the sturgeons are often found full of the little fishes, which they have taken in by their sucker-like mouths. At the time of the runs the eulachon are extremely fat, so much so that it is said that when dried and a wick drawn through the body they may be used as candles. On Nass River, in British Columbia, a stream in which their run is greatest, there is a factory for the manufacture of eulachon-oil from them. This delicate oil is proposed as a substitute for cod-liver oil in medicine. Whatever may be its merits in this regard, it has the disadvantage in respect to salability of being semi-solid or lard-like at ordinary temperatures, requiring melting to make it flow as oil. The eulachon is a favorite pan-fish in British Columbia. The writer has had considerable experience with it, broiled and fried, in its native region, and has no hesitation in declaring it to be the best-flavored food-fish in American waters. It is fat, tender, juicy, and richly flavored, with comparatively few troublesome bones. It does not, however, bear transportation well. The Indians in Alaska bury the eulachon in the ground in great masses. After the fish are well decayed they are taken out and the oil pressed from them. The odor of the fish and the oil is then very offensive, less so, however, than that of some forms of cheese eaten by civilized people.

The capelin (Mallotus villosus) closely resembles the eulachon, differing mainly in its broader pectorals and in the peculiar scales of the males. In the male fish a band of scales above the lateral line and along each side of the belly become elongate, closely imbricated, with the free points projecting, giving the body a villous appearance. It is very abundant on the coasts of Arctic America, both in the Atlantic and the Pacific, and is an important source of food for the natives of those regions.

This species spawns in the surf, and the writer has seen them in August cast on the shores of the Alaskan islands (as at Metlakahtla in 1897), living and dead, in numbers which seem incredible. The males are then distorted, and it seems likely that all of them perish after spawning. The young are abundant in all the northern fiords. Even more inordinate numbers are reported from the shores of Greenland.

The capelin seems to be inferior to the eulachon as a food-fish, but to the natives of arctic regions in both hemispheres it is a very important article of food. Fossil capelin are found in abundance in recent shales in Greenland enveloped in nodules of clay. In the open waters about the Aleutian Islands a small smelt, Therobromus callorhini, occurs in very great abundance and forms the chief part of the summer food of the fur-seal. Strangely enough, no complete specimen of this fish has yet been seen by man, although thousands of fragments have been taken from seals' stomachs. From these fragments Mr. Frederick A. Lucas has reconstructed the fish, which must be an ally of the surf-smelt, probably spawning in the open ocean of the north.

The silvery species called Argentina live in deeper water and have no commercial importance. Argentina silus, with prickly scales, occurs in the North Sea. Several fossils have been doubtfully referred to Osmerus.

The Microstomidæ.—The small family of Microstomidæ consists of a few degraded smelt, slender in form, with feeble mouth and but three or four branchiostegals, rarely taken in the deep seas. Nansenia grœnlandica was found by Reinhardt off the coast of Greenland, and six or eight other species of Microstoma and Bathylagus have been brought in by the deep-sea explorations.

The Salangidæ, or Icefishes.—Still more feeble and insignificant are the species of Salangidæ, icefishes, or Chinese whitebait, which may be described as Salmonidæ reduced to the lowest terms. The body is long and slender, perfectly translucent, almost naked, and with the skeleton scarcely ossified. The fins are like those of the salmon, the head is depressed, the jaws long and broad, somewhat like the bill of a duck, and within there are a few disproportionately strong canine teeth, those of the lower jaw somewhat piercing the upper. The alimentary canal is straight for its whole length, without pyloric cæca. These little fishes, two to five inches long, live in the sea in enormous numbers and ascend the rivers of eastern Asia for the purpose of spawning. It is thought by some that they are annual fishes, all dying in the fall after reproduction, the species living through the winter only within its eggs. But this is only suspected, not proved, and the species will repay the careful study which some of the excellent naturalists of Japan are sure before long to give to it. The species of Salanx are known as whitebait, in Japan as Shiro-uwo, which means exactly the same thing. They are also sometimes called icefish (Hingio), which, being used for no other fish, may be adopted as a group name for Salanx.

The species are Salanx chinensis from Canton, Salanx hyalo cranius from Korea and northern China, Salanx microdon from northern Japan, and Salanx ariakensis from the southern island of Kiusiu. The Japanese fishes are species still smaller and feebler than their relatives from the mainland.

The Haplochitonidæ.—The Haplochitonidæ are trout-like fishes of the south temperate zone, differing from the Salmonidæ mainly in the extension of the premaxillary until, as in the perch-like fishes, it forms the outer border of the upper jaw. The adipose fin is present as in all the salmon and smelt. Haplochiton of Tierra del Fuego and the Falkland Islands is naked, while in Prototroctes of Australia and New Zealand the body, as in all salmon, trout, and smelt, is covered with scales. Prototroctes maræna is the yarra herring of Australia. The closely related family of Galaxiidæ, also Australian, but lacking the adipose fin, is mentioned in a later chapter.

Stomiatidæ.—The Stomiatidæ, with elongate bodies, have the mouth enormous, with fang-like teeth, usually barbed. Of the several species Stomias ferox is best known. According to Dr. Boulenger, these fishes are true Isospondyli.

Astronesthidæ is another small group of small fishes naked and black, with long canines, found in the deep sea.

The Malacosteidæ is a related group with extremely distensible mouth, the species capable of swallowing fishes much larger than themselves.

The viper-fishes (Chauliodontidæ) are very feeble and very voracious little fishes occasionally brought up from the depths. Chauliodus sloanei is notable for the length of the fangs.

Much smaller and feebler are the species of the closely related family of Gonostomidæ. Gonostoma and Cyclothone dwell in oceanic abysses. One species, Cyclothone elongata, occurs at the depth of from half a mile to nearly four miles almost everywhere throughout the oceans. It is probably the most widely distributed, as well as one of the feeblest and most fragile, of all bassalian or deep-sea fishes.

Suborder Iniomi, the Lantern-fishes.—The suborder Iniomi (ἰνίον, nape; ὤμος, shoulder) comprises soft-rayed fishes, in which the shoulder-girdle has more or less lost its completeness of structure as part of the degradation consequent on life in the abysses of the sea. These features distinguish these forms from the true Isospondyli, but only in a very few of the species have these characters been verified by actual examination of the skeleton. The mesocoracoid arch is wanting or atrophied in all of the species examined, and the orbitosphenoid is lacking, so far as known. The group thus agrees in most technical characters with the Haplomi, in which group they are placed by Dr. Boulenger. On the other hand the relationships to the Isospondyli are very close, and the Iniomi have many traits suggesting degenerate Isospondyli. The post-temporal has lost its usual hold on the skull and may touch the occiput on the sides of the cranium. Nearly all the species are soft in body, black or silvery over black in color, and all that live in the deep sea are provided with luminous spots or glands giving light in the abysmal depths. These spots are wanting in the few shore species, as also in those which approach most nearly to the Salmonidæ, these being presumably the most primitive of the group. In these also the post-temporal touches the back of the cranium near the side. In the majority of the Iniomi the adipose fin of the Salmonidæ is retained. From the phosphorescent spots is derived the general name of lantern-fishes applied of late years to many of the species. Most of these are of recent discovery, results of the remarkable work in deep-sea dredging begun by the Albatross and the Challenger. All of the species are carnivorous, and some, in spite of their feeble muscles, are exceedingly voracious, the mouth being armed with veritable daggers and spears.

Aulopidæ.—Most primitive of the Iniomi is the family of Aulopidæ, having an adipose fin, a normal maxillary, and no luminous spots. The rough firm scales suggest those of the berycoid fishes. The few species of Aulopus and Chlorophthalmus are found in moderate depths. Aulopus purpurissatus is the "Sergeant Baker" of the Australian fishermen.

The Lizard-fishes.—The Synodontidæ, or lizard-fishes, have lizard-like heads with very large mouth. The head is scaly, a character rare among the soft-rayed fishes. The slender maxillary is grown fast to the premaxillary, and the color is not black. Most of the species are shore-fishes and some are brightly colored. Synodus fætens is the common lizard-fish, or galliwasp, of our Atlantic coast. Synodus varius of the Pacific is brightly colored, olive-green and orange-red types of coloration existing at different depths. Most of the species lie close to the bottom and are mottled gray like coral sand. A few occur in oceanic depths. The "Bombay duck" of the fishermen of India is a species of Harpodon, H. nehereus, with large mouth and arrow-shaped teeth. The dried fish is used as a relish.

The Benthosauridæ are deep-sea fishes of similar type, but with distinct maxillaries. The Bathypteroidæ, of the deep seas, resemble Aulopus, but have the upper and lower pectoral rays filiform, developed as organs of touch in the depths in which the small eyes become practically useless.

Ipnopidæ.—In the Ipnopidæ the head is depressed above and the two eyes are flattened and widened so as to occupy most of its upper surface. These structures were at first supposed to be luminous organs, but Professor Moseley has shown them to be eyes. "They show a flattened cornea extending along the median line of the snout, with a large retina composed of peculiar rods which form a complicated apparatus destined undoubtedly to produce an image and to receive especial luminous rays." The single species, Ipnops murrayi, is black in color and found at the depth of 2½ miles in various seas.

The existence of well-developed eyes among fishes destined to live in the dark abysses of the ocean seems at first contradictory, but we must remember that these singular forms are descendants of immigrants from the shore and from the surface. "In some cases the eyes have not been specially modified, but in others there have been modifications of a luminous mucous membrane leading on the one hand to phosphorescent organs more or less specialized, or on the other to such remarkable structures as the eyes of Ipnops, intermediate between true eyes and phosphorescent plates. In fishes which cannot see, and which retain for their guidance only the general sensibility of the integuments and the lateral line, these parts soon acquire a very great delicacy. The same is the case with tactile organs (as in Bathypterois and Benthosaurus), and experiments show that barbels may become organs of touch adapted to aquatic life, sensitive to the faintest movements or the slightest displacement, with power to give the blinded fishes full cognizance of the medium in which they live."

Rondeletiidæ.—The Rondeletiidæ are naked black fishes with small eyes, without adipose fin and without luminous spots, taken at great depths in the Atlantic. The relationship of these fishes is wholly uncertain.

The Cetomimidæ are near allies of the Rondeletiidæ, having the mouth excessively large, with the peculiar form seen in the right whales, which these little fishes curiously resemble.

Myctophidæ.—The large family of Myctophidæ, or lantern-fishes, is made up of small fishes allied to the Aulopidæ, but with the body covered with luminous dots, highly specialized and symmetrically arranged. Most of them belong to the deep sea, but others come to the surface in the night or during storms when the sunlight is absent. Through this habit they are often thrown by the waves on the decks of small vessels. Largely from Danish merchant-vessels, Dr. Lütken has obtained the unrivaled collection of these sea-waifs preserved in the Museum of the University of Copenhagen. The species are all small in size and feeble in structure, the prey of the larger fishes of the depths, from which their lantern-like spots and large eyes help them to escape. The numerous species are now ranged in about fifteen genera, although earlier writers placed them all in a single genus Myctophum (Scopelus).

In the genus Diaphus (Æthoprora) there is a large luminous gland on the end of the short snout, like the headlight of an engine. In Dasyscopelus the scales are spinescent, but in most of the genera, as in Myctophum, the scales are cycloid and caducous, falling at the touch. In Diaphus the luminous spots are crossed by a septum giving them the form of the Greek letter θ (theta). One of the commonest species is Myctophum humboldti.

Chirothricidæ.—The remarkable extinct family of Chirothricidæ may be related to the Synodontidæ, or Myctophidæ. In this group the teeth are feeble, the paired fins much enlarged, and the ventrals are well forward. The dorsal fin, inserted well forward, has stout basal bones. Chirothrix libanicus of the Cretaceous of Mt. Lebanon is remarkable for its excessively large ventral fins. Telepholis is a related genus. Exocœtoides with rounded caudal fin is probably the type of a distinct family, Exocœtoididæ, the caudal fin being strongly forked in Chirothrix. The small extinct group of Rhinellidæ is usually placed near the Myctophidæ. They are distinguished by the very long gar-like jaws; whether they possessed adipose fins or luminous spots cannot be determined. Rhinellus furcatus and other species occur in the Cretaceous of Europe and Asia. Fossil forms more or less distinctly related to the Myctophidæ are numerous. Osmeroides monasterii (wrongly called Sardinioides), from the German Cretaceous, seems allied to Myctophum, although, of course, luminous spots leave no trace among fossils. Acrognathus boops is remarkable for the large size of the eyes.

Maurolicidæ.—The Maurolicidæ are similar in form and habit, but scaleless, and with luminous spots more highly specialized. Maurolicus pennanti, the "Sleppy Argentine," is occasionally taken on either side of the Atlantic. Other genera are Zalarges, Vinciguerria, and Valenciennellus.

The Lancet-fishes.—The Plagyodontidæ (Alepisauridæ) contains the lancet-fishes, large, swift, scaleless fishes of the ocean depths with very high dorsal fin, and the mouth filled with knife-like teeth. These large fish are occasionally cast up by storms or are driven to the shores by the torments of a parasite, Tetrarhynchus, found imbedded in the flesh.

It is probable that they are sometimes killed by being forced above their level by fishes which they have swallowed. In such cases they are destroyed through the reduction of pressure.

Every part of the body is so fragile that perfect specimens are rare. The dorsal fin is readily torn, the bones are very feebly ossified, and the ligaments connecting the vertebræ are very loose and extensible, so that the body can be considerably stretched. "This loose connection of the parts of the body is found in numerous deep-sea fishes, and is merely the consequence of their withdrawal from the pressure of the water to which they are exposed in the depths inhabited by them. When within the limits of their natural haunts, the osseous, muscular, and fibrous parts of the body will have that solidity which is required for the rapid and powerful movements of a predatory fish. That the fishes of this genus (Plagyodus) belong to the most ferocious of the class is proved by their dentition and the contents of their stomach." (Günther.) Dr. Günther elsewhere observes: "From the stomach of one example have been taken several octopods, crustaceans, ascidians, a young Brama, twelve young boarfishes (Capros), a horse-mackerel, and one young of its own species."

The lancet-fish, Plagyodus ferox, is occasionally taken on either side of the Atlantic and in Japan. The handsaw-fish, called Plagyodus æsculapius, has been taken at Unalaska, off San Luis Obispo, and in Humboldt Bay. It does not seem to differ at all from Plagyodus ferox. The original type from Unalaska had in its stomach twenty-one lumpfishes (Eumicrotremus spinosus). This is the species described from Steller's manuscripts by Pallas under the name of Plagyodus. Another species, Plagyodus borcalis, is occasionally taken in the North Pacific.

The Evermannellidæ is a small family of small deep-sea fishes with large teeth, distensible muscles, and an extraordinary power of swallowing other fishes, scarcely surpassed by Chiasmodon or Saccopharynx. Evermannella (Odontostomus, the latter name preoccupied) and Omosudis are the principal genera.

The Paralepidæ are reduced allies of Plagyodus, slender, silvery, with small fins and fang-like jaws. As in Plagyodus, the adipose fin is developed and there are small luminous dots. The species are few and mostly northern; one of them, Sudis ringens, is known only from a single specimen taken by the present writer from the stomach of a hake (Merluccius productus), the hake in turn swallowed whole by an albacore in the Santa Barbara Channel. The Sudis had been devoured by the hake, the hake by the albacore, and the albacore taken on the hook before the feeble Sudis had been digested.

Perhaps allied to the Plagyodontidæ is also the large family of Enchodontidæ, widely represented in the Cretaceous rocks of Syria, Europe, and Kansas. The body in this group is elongate, the teeth very strong, and the dorsal fin short. Enchodus lewesiensis is found in Mount Lebanon, Halec sternbergi in the German Cretaceous, and many species of Enchodus in Kansas; Cimolichthys dirus in North Dakota.

Remotely allied to these groups is the extinct family of Dercetidæ from the Cretaceous of Germany and Syria. These are elongate fishes, the scales small or wanting, but with two or more series of bony scutes along the flanks. In Dercetis scutatus the scutes are large and the dorsal fin is very long. Other genera are Leptotrachelus and Pelargorhynchus. Dr. Boulenger places the Dercetidæ in the order Heteromi. This is an expression of the fact that their relations are still unknown. Probably related to the Dercetidæ is the American family of Stratodontidæ with its two genera, Stradodus and Empo from the Cretaceous (Niobrara) deposits of Kansas. Empo nepaholica is one of the best-known species.

The Sternoptychidæ.—The Sternoptychidæ differ materially from all these forms in the short, compressed, deep body and distorted form. The teeth are small, the body bright silvery, with luminous spots. The species live in the deep seas, rising in dark or stormy weather. Sternoptyx diaphana is found in almost all seas, and species of Argyropelecus are almost as widely distributed. After the earthquakes in 1896, which engulfed the fishing villages of Rikuzen, in northern Japan, numerous specimens of this species were found dead, floating on the water, by the steamer Albatross.

The Idiacanthidæ are small deep-sea fishes, eel-shaped and without pectorals, related to the Iniomi.

Order Lyopomi.—Other deep-sea fishes constitute the order or suborder Lyopomi (λυός, loose; πῶμα, opercle). These are elongate fishes having no mesocoracoid, and the preopercle rudimentary and connected only with the lower jaw, the large subopercle usurping its place. The group, which is perhaps to be regarded as a degenerate type of Isospondyli, contains the single family of Halosauridæ, with several species, black in color, soft in substance, with small teeth and long tapering tail, found in all seas. The principal genera are Halosaurus and Aldrovandia (Halosauropsis). Aldrovandia macrochira is the commonest species on our Atlantic coast.

Several fossil Halosauridæ are described from the Cretaceous of Europe and Syria, referred to the genera Echidnocephalus and Enchelurus. Boulenger refers the Lyopomi to the suborder Heteromi.