Chapter XXII: Appendix: To the Fishes: Palaeospondylidae—ostracodermi—heterostraci (3)

Cope believed an orifice at or above the axil of the pectoral fin in _Noturus_ to be the opening of the duct of a poison-gland; "from it may frequently be drawn a solid gelatinous style ending in a tripod, each limb of which is dichotomously divided into short branches of regular length." I think this condition of things has nothing to do with a poison-organ, and is merely a repetition of what is observed in Loaches and in the Characinid _Xenocharax_, where I have found a gelatinous substance filling the short duct by which the membrane of the air-bladder is placed in communication with the skin and the sensory organ of the lateral line. Most Silurids can live in very foul water, taking in air from the surface, and spend a comparatively long time out of the water, without being possessed of any special apparatus for atmospheric respiration. A few genera, however, are provided with an accessory breathing organ: in _Clarias_, _Heterobranchus_, and allies, there is a dendritic superbranchial organ, in _Saccobranchus_ a long air-sac, extending from the first branchial cleft along the side of the body, as described above, p. 295; and these Fish can live for days on land. _Clarias lazera_ has been observed, in Senegambia, to spend several months of the dry season in burrows, from which it emerges at night to crawl about in search of food. Many Silurids, but especially _Doras_ and _Synodontis_, are known to produce sounds in and out of the water by means of a special mechanism of the air-bladder and the processes of the vertebrae above it, combined with the movements of the pectoral spine grinding in the glenoid cavity.[672] In South America, _Doras_ has been observed to move rapidly on land, projecting itself forward on the pectoral spines by the elastic spring of the tail, travelling long journeys over land, from one drying pond to another, spending whole nights on the way; these migrations sometimes take place {591}in numerous bands, baskets of the small Fish being filled by the Indians who come across them.[673] The African _Synodontis_ are much in the habit of floating or swimming leisurely on the surface with the belly in the air, as was well known to the ancient Egyptians, who have frequently depicted the Fish in this anomalous position. A curious fact in connexion with this habit is that _S. membranaceus_ and _S. batensoda_, in which it has most frequently been observed, show an inversion of the ordinary mode of coloration, the lower parts being dark brown or black and the upper pale silvery grey. The electric Cat-Fish (_Malopterurus electricus_), is also a native of Africa, occurring all over the tropical parts of that continent and also in the Lower Nile, growing to a length of three feet. Its flesh is more esteemed than that of other Silurids. It avoids light and is slow in its movements. The electrical apparatus differs absolutely from that of all other Fishes, being derived from the integument, belonging to the glandular system, and surrounding the whole body with a thick coat of grease or gelatinous substance; the apparatus is governed by a single nerve on each side proceeding from a huge ganglionic cell at the anterior extremity of the spinal cord.[674] The shocks given by _Madopterurus_ are very powerful, and the Fish is called "Raad" by the Arabs, a name which means "thunder." Kept in an aquarium with other Fishes, even of the same species, the "Raad" soon kills its companions.

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In this family the eggs and young are usually looked after by the parents. Aristotle observed that the male of the European _Silurus glanis_ watches over and defends the eggs. In one of the commonest North American Cat-Fishes, _Amiurus nebulosus_, a species which has been largely introduced into some parts of Europe of late, now thriving in many ponds and more or less polluted streams of the Continent, the eggs are deposited near the banks of weedy ponds and rivers without currents, in concealed places beneath logs, stumps, or even in pails or other receptacles, failing which both parents join in excavating a sort of nest in the mud, a work often requiring two or three days of incessant labour. The male watches over the eggs, and later leads the young in great schools near the shore, seemingly caring for them as the hen for her chickens.[675] The _Doras_ and the _Callichthys_ of South America, according to Hancock[676] and Vipan,[677] build regular nests of grass or leaves, sometimes placed in a hole scooped out in the bank, in which they cover their eggs and defend them, male and female sharing in this parental duty. In the likewise South American _Corydoras_ (_Callichthys paleatus_), as observed by Carbonnier,[678] a lengthy courtship takes place, followed by an embrace, during which the female receives the seminal fluid in a sort of pouch formed by the folded membranes of her ventral fins; immediately after, five or six eggs are produced and received in the pouch, to be afterwards carefully placed in a secluded spot. This operation is repeated many times, until the total number of eggs, about 250, have been deposited. In {593}accordance with these pairing habits, the pectoral spines of the male, which are used in amplexation, are longer and stronger than those of the female. These Fish are monogamous, and both parents remain by the side of the nest, furiously attacking any assailant. Dr. R. Semon[679] has made observations in Queensland on the habits of _Arius australis_, which builds nests in the sandy bed of the Burnett River. These nests consist of circular basin-like excavations, about 20 inches in diameter, at the bottom of which the eggs are laid, and covered over by several layers of large stones. A still more efficient protection is afforded their progeny by the marine and estuarine species of _Arius_,[680] _Galeichthys_,[681] and _Osteogeniosus_,[682] the male, more rarely the female, carrying the eggs in the mouth and pharynx; these eggs, few in number, are remarkably large, measuring as much as 17 or 18 millimetres in diameter in _Arius commersonii_, a Fish of three or four feet in length. According to Babuchin, _Malopterurus_ also is said by the Nile fishermen to shelter its fry in the mouth.

Some of the Silurids attain to a very large size. Among these is the type of the family, _Silurus glanis_, the "Wels" of the Germans, its only European representative, which occurs over a great part of Europe, but is absent from the British Isles, France, the Spanish Peninsula, and Italy. It is most abundant in the Danube basin, where it sometimes reaches a length of 10 feet or more and a weight of 400 lbs. It is the largest strictly fresh-water Fish of Europe. Among the smallest species, we have to mention the "Candiru" of Brazil, _Vandellia cirrhosa_, 60 millimetres in length and 3 or 4 in diameter, which is believed to enter and ascend the urethra of people bathing, being attracted by the urine; the Fish, having once made its way into the urethra, cannot be pulled out again, owing to the erectile spines which arm its gill-covers. The natives of some parts of the Amazons are in great dread of this Fish, and protect themselves when entering the water by wearing a sheath formed of a small, minutely-perforated cocoanut-shell suspended from a belt of palm-fibres.[683] According {594}to Reinhardt[684] the allied _Stegophilus insidiosus_, a small colourless Fish, 30 to 40 mm. long, from Brazil and Argentine, lives parasitically in the gill-cavity of large Cat-Fishes (_Platystoma_). Dr. F. Silvestri has noticed that it sucks the blood in the gills of _Platystoma coruscans_, a Silurid growing to a length of 6 feet.

FAM. 5. LORICARIIDAE.—Distinguished from the preceding by the sessile ribs and the absence of the transverse processes in the praecaudal vertebrae, which have bifid neural spines. The air-bladder is always much reduced, and enclosed in a right and a left bony capsule formed by the skull and the anterior vertebrae. Gill-openings narrow clefts. The mouth is inferior, with more or less developed circular lips and feeble dentition; it is used as a sucker, by which the Fish fixes itself to any hard object with such strength that it cannot be pulled off without great difficulty. The teeth are usually slender and bicuspid. The food consists of very small prey and more or less putrefied organic substances, the intestine being usually extremely elongate and much convoluted. The habits of these Fish are very little known, but the fact that the males of many species have the pectoral fins much stronger than the females renders it probable that they pair like {595}_Callichthys_. There are other sexual differences in many species of _Plecostomus_, _Chaetostomus_, and _Loricaria_, as the presence of dermal tentacles on the snout (see Fig. 359), or of hair-like bristles on various parts of the head and fins in the males, which are usually of larger size.

About 200 species are known, all from the tropical and subtropical parts of Central and South America. The largest species (_Chaetostomus gigas_) measures 2½ feet; many are of very small size.[685] The genera may be referred to two sub-families:—

(i.) ARGINAE.—Body naked; ribs strong. _Arges_, _Stygogenes_, _Astroblepus_.

(ii.) LORICARIINAE.—Body cuirassed by bony plates; ribs very slender. _Plecostomus_, _Liposarcus_, _Chaetostomus_, _Cochliodon_, _Pterygoplichthys_, _Rhinelepis_, _Acanthicus_, _Otocinclus_, _Hypoptopoma_, _Loricaria_, _Acestra_.

The "Prenadillas" of the Andes, _Arges_ and _Stygogenes_, were believed to live in subterranean waters within the bowels of active volcanoes, and to be ejected with streams of mud and water during eruptions, a story that has been repeated by Humboldt. The fact is that they live in small torrents at great altitudes (up to 10,700 feet), and are swept down during periods of disturbance caused by the eruption of the volcano.[686] The members of the sub-family Loricariinae vary much in the shape of the body, which may be short and stout, or more or less slender, the extreme in the latter respect being attained by the species of the genus _Acestra_.

{596}FAM. 6. ASPREDINIDAE.—This family is also closely related to the Siluridae. The ribs are sessile as in the Loricariidae, but inserted very low down on the centra, which higher up bear strong transverse processes. The opercular bone is entirely absent. The gill-opening is reduced to a foramen in front of the pectoral fin. The head is extremely depressed and the mouth terminal; the tail is very slender; the body is naked. The air-bladder is large and free, the intestinal canal short. Four genera from South America: _Aspredo_, _Bunocephalus_, _Bunocephalichthys_, _Dysichthys_. Species 18. _Aspredo_, of the Guianas, the largest form, reaching to about a foot in length, is remarkable for the manner in which the female carries her eggs. The skin of the lower parts assumes a spongy condition about the breeding season, and the eggs, after being deposited, become attached to the lower surface of the head, belly, and paired fins, forming a single layer; each egg becomes connected with the skin of the mother by a cup-shaped, pedunculate base, supplied with blood-vessels and coated with a layer of epithelium, the formation of which is still unexplained.[687]

{597}CHAPTER XXII

TELEOSTEI (_CONTINUED_): SYMBRANCHII—APODES—HAPLOMI—HETEROMI—CATOSTEOMI— PERCESOCES—ANACANTHINI

SUB-ORDER 3. SYMBRANCHII

Eel-shaped Fishes without paired fins, with the pectoral arch free or suspended from the skull, and with the anterior vertebrae distinct, without Weberian ossicles. Gill-openings confluent into a single, ventral slit. Air-bladder absent.

The structure of the skull conforms to that of typical Malacopterygians. The praemaxillary and maxillary are well developed, the latter placed behind the former, and forming but a very small part of the oral border; the symplectic is present; the parietals form a long sagittal suture, and separate the frontals from the supraoccipital. The vertebrae are very numerous, the praecaudal bearing very strong parapophyses, to which short, slender ribs are attached. The skin is naked (Symbranchidae) or covered with minute scales (Amphipnoidae), and the vertical fins are rudimentary, reduced to mere dermal folds.

Like the Apodes, which they resemble in general appearance, these Fishes are no doubt derived from some low type with abdominal ventral fins, but whether from the Malacopterygii or the Haplomi we have as yet no data from which to conclude. Only two families are known.

FAM. 1. SYMBRANCHIDAE.—Post-temporal well developed, forked, attached to the skull. Inhabitants of the fresh or brackish waters of South-Eastern Asia, Tropical America, Australia, and Tasmania. Three genera are known: _Symbranchus_, with two species from India and the Malay region, and one from Central and South America; _Monopterus_, with a single species {598}from China, Japan, and the Malay region; and _Chilobranchus_, with two species from Australia and Tasmania. Although the South American _Symbranchus_ has been observed to live in marshes which periodically dry up, the Fish burying itself in the mud like a _Lepidosiren_, the branchiae are fully developed on the four branchial arches. In _Monopterus_, of similar habits, the branchial laminae are rudimentary, and on three arches only. No accessory breathing organ is known to exist.

FAM. 2. AMPHIPNOIDAE.—Post-temporal absent, the shoulder-girdle free from the skull. The Cuchia, _Amphipnous cuchia_, the sole representative of this family, an inhabitant of the fresh and brackish waters of India and Burma, growing to two feet in length, is remarkable for the presence of a respiratory air-sac on each side of the neck behind the head, communicating with the gill-cavity. Of the three branchial arches the second alone possesses gill-filaments; the third supports, in their place, a thick and semi-transparent tissue; the principal organs of respiration are two small bladders, resembling the posterior portions of the lungs of snakes, which the animal has the power {599}of filling with air immediately derived from the atmosphere. Although covered over by the common integuments, these bladders present externally, when inflated, two protuberances of a round shape. Of the whole volume of blood contained in the branchial artery, one-third passes through the gills and respiratory bladders, whilst the other two-thirds are conveyed directly from the heart to the aorta without being exposed to the action of the air.[688] This amphibious Fish, when in the water, constantly rises to the surface for the purpose of respiration, and it is often found lying in the grassy sides of ponds after the manner of Snakes.

SUB-ORDER 4. APODES.

Air-bladder, if present, communicating with the digestive tract by a duct. Praemaxillaries absent; the maxillaries, if present, separated on the median line by the coalesced ethmoid and vomer. Pectoral arch, if present, not connected with and remote from the skull; mesocoracoid arch absent. Fins without spines, the ventrals absent. Anterior vertebrae distinct, without Weberian ossicles.

The Apodes or Eels are elongate, serpentiform Fishes with naked skin, or with minute scales imbedded in the skin, the opercular bones small and completely hidden under the integument; narrow or minute gill-openings; the vertical fins, if present, confluent behind or separated by the projecting tip of the tail. The pterygo-palatine arch is often reduced or absent, and there is no distinct symplectic; the supraoccipital bone is small, separated from the frontals by the parietals, which meet on the middle line. The vertebrae are very numerous (up to 225), and the praecaudals bear strong parapophyses, to which short, slender ribs may be attached; epineurals are sometimes present. The five families into which this sub-order is divided show remarkable degrees of simplification of the skull, through reduction or loss of either the maxillary or the pterygo-palatine arches.

There has been much difference of opinion in the determination of the bones of the upper jaw in these Fishes. Cuvier regarded the lateral bones of the upper jaw as praemaxillaries, Owen and Richardson as palatines (at least in Muraenas), whilst Peters {600}and most recent authors have identified them throughout the order as maxillaries.[689] The conclusion I have come to from the examination of numerous skulls belonging to various genera, is that the praemaxillaries have disappeared in all, whilst the maxillaries have persisted in the true Eels (Anguillidae) and disappeared in the Muraenidae, their place being taken by the fused palato-ectopterygoids, which may even join the mandibular suspensorium. The vestigial bone, regarded by Jacoby as the pterygoid in _Muraena helena_, may be identified as the meta-pterygoid, and therefore does not disprove the homology, here suggested, of the other elements of the palate.

FAM. 1. ANGUILLIDAE.—Maxillaries present, separated on the median line by the ethmo-vomer; palato-pterygoid bone present, connected with the hyomandibular and quadrate; gill-clefts separate, opening into the pharynx by wide slits; tongue present; vent far removed from the head.

Spread over all the seas of the temperate and tropical zones, often descending to the greatest depths, a few entering fresh waters. Many are known to undergo very striking metamorphoses, the pellucid, strongly compressed larvae (_Leptocephalus_) having long been a puzzle to naturalists.

{601}Nearly 150 recent species are known, of which some 50 are deep-sea forms, occurring down to 2500 fathoms. Scanty fossil remains, referable to recent genera or scarcely different from them, are known from the Eocene of Europe. The Cretaceous genus _Urenchelys_, from England and the Lebanon, is interesting as representing a more generalised type, the hindmost vertebrae bearing a pair of expanded hypural bones, showing the diphycercal Eels to have been derived from Fishes with a normal caudal fin.

The genera are numerous. The following are the principal:—_Anguilla_, _Simenchelys_, _Ilyophis_, _Conger_, _Coloconger_, _Congromuraena_, _Uroconger_, _Heteroconger_, _Muraenesox_, _Nettastoma_, _Nettophichthys_, _Saurenchelys_, _Nettenchelys_, _Myrus_, _Myrophis_, _Derichthys_, _Chilorhinus_, _Muraenichthys_, _Liuranus_, _Ophichthys_, _Moringua_.

In the first four genera, small, more or less lineal rudimentary scales are embedded in the skin, arranged in small groups, which are placed obliquely at right angles to one another, forming a curious pattern; but these scales are so small that they escape the notice of the superficial observer, hence Eels have been improperly included among the Fishes forbidden as food by the Mosaic prescriptions. In the other genera, including the exclusively marine Conger of our coasts, scales are really absent.

The Common Eel (_Anguilla vulgaris_) has a very wide distribution, being found over the greater part of Europe, North Africa, Temperate Asia, and perhaps also North America east of the Rocky Mountains, Mexico, and the West Indies. Its record from Australia and New Zealand is probably due to the imperfection of our knowledge of the specific characters. It is not found in the Black Sea nor in the rivers flowing into it, owing, no doubt, to the sulphurous nature of the bottom of the sea, to which, as we now know, these Fish would have to resort for breeding.

The mode of propagation of the Eel long remained a mystery, from the fact that individuals found in fresh water never show ripe genital glands. The idea had been entertained of their being hermaphrodite, and internal parasites had also given rise to the belief in their viviparous nature. The genital glands of the female were first investigated by Rathke in 1838, but it was not until 1874 that those of the male were discovered by Syrski, and shortly after fully described by L. Jacoby, who, in his final contribution to the subject, concluded that Eels need salt water for the development of their organs of generation, and that this development takes place, not near the coast, but further out in deep water.

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As a rule it is not until the fifth or sixth year that the Eels go to the sea for the purpose of propagation, which takes place at great depths—at least 200 fathoms. Males have been observed to precede the females. The breeding season over, the Eels do not return to fresh waters, but are believed to die soon after. The eggs were discovered by Raffaele in 1888 in the Gulf of Naples, and shortly after Grassi and Calandruccio finally settled the question of the breeding and development of the Fish from observations made in the Mediterranean. Their conclusions are thus summed up:—"The Common Eel matures in the depths of the sea, where it acquires larger eyes than are ever observed in individuals which have not yet migrated to deep water. The abysses of the sea are its spawning places; its eggs float in the sea water. In developing from the egg, it undergoes a metamorphosis, it passes through a larval form denominated _Leptocephalus brevirostris_." What length of time the development requires is not yet fully established, since the Leptocephali are rarely found at the surface, most of the specimens studied by Grassi and Calandruccio having been obtained from the stomach of the Sun-Fish (_Orthagoriscus mola_) in the Straits of Messina; but it is believed that the young Eels or "elvers," which ascend our rivers in such prodigious numbers in spring and summer ("Eel-Fares") are already one year old. Some individuals apparently spend their whole life in fresh waters, but they are barren.[690] A specimen was kept in confinement in the family of the French naturalist Desmarest for upwards of 40 years, growing to a length of 4½ feet, being already of large size at the time of {603}its capture. Eels are extremely voracious, and endowed with an extraordinary tenacity of life; they can live for many hours out of the water, and are often met with at night creeping through the grass of meadows from one pond or stream to another.

One of the most remarkable among the deep-sea Eels is the Snub-nosed Eel (_Simenchelys parasiticus_), which has been found in great numbers off Newfoundland and the Azores, at depths of 200 to 900 fathoms. The maxillary and mandibular bones are very short and massive, provided with large obtuse teeth; the head is short and bulldog-like in aspect, the mouth small and bordered by a thick circular lip. Some specimens have been observed to burrow in the muscles of living Halibut and other large Fishes, after the manner of _Myxine_.

FAM. 2. NEMICHTHYIDAE.—Distinguished from the preceding by the position of the vent, which is close to, or at no great distance from, the gill-openings. The rays of the vertical fins are connected by thin membrane instead of being imbedded in thick skin, as in most Eels; in some of the genera the jaws are excessively prolonged, needle-like, sometimes recurved. Deep-sea Eels of small size, represented in the Atlantic, Pacific, and Indian Oceans by about 10 species, referred to 6 genera: _Dysomma_, _Dysommatopsis_, _Nemichthys_, _Spinivomer_, _Serrivomer_, _Gavialiceps_.

FAM. 3. SYNAPHOBRANCHIDAE.—Maxillaries narrowly separated on the median line, their extremity strongly attached by ligament to the mandible; pterygo-palatine arch absent. Gill-openings externally confluent into a single ventral slit. Deep-sea Fishes, resembling the true Eels in the general form and in the presence of linear scales placed at right angles, but differing in the absence of the pterygo-palatine arch, as in the Saccopharyngidae. Eight species of _Synaphobranchus_ are known, from the Atlantic, Pacific, and Indian Oceans, at depths of 200 to 2000 fathoms.

FAM. 4. SACCOPHARYNGIDAE.—Maxillaries narrowly separated on the median line, extremely elongate; mouth enormous; pterygo-palatine arch absent; hyomandibular arch slender and movably articulated to the cranium, the two bones (hyomandibular and quadrate) of which it is composed being capable of being swung in all directions; branchial arches far behind the skull; no branchiostegal rays or pharyngeal bones.

Extraordinary-looking deep-sea Fishes allied to the Eels, of which they appear to be a further degraded type, the muscles {604}being feebly developed and the skeleton imperfectly calcified. The mouth, furnished with rather long but feeble, or even minute teeth, and the pharynx and stomach are capable of great distension, these Fish being able to get outside a prey very much larger than themselves; the eyes are situated far forward on the head; the tail is extremely slender and elongate. Four genera are known, each with a single species, from the Atlantic: _Saccopharynx_, _Eurypharynx_, _Macropharynx_, and _Gastrostomus_. The depths at which they have been obtained vary between 389 and 1467 fathoms, but three out of the four known specimens of _Saccopharynx_ were brought to the surface by having swallowed a Fish too large for the capacity of the stomach. The length of the largest specimen is about 6 feet, of which the tail constitutes nearly three-fourths.

FAM. 5. MURAENIDAE.—Maxillaries absent, replaced by the palato-pterygoid, the mouth bordered by the latter and the {605}ethmo-vomer; palato-pterygoid bone separated from hyomandibular arch; branchial openings into the pharynx narrow slits; no tongue.

The body is naked, pectoral fins are usually absent, and the gill-cleft is a small round opening. The opercular bones are much reduced in size, and the pectoral arch may be totally absent.

Voracious marine Fishes, inhabiting tropical and subtropical waters, being especially abundant about coral reefs. Some 120 species are known, many reaching a very large size, and being also remarkable for their variegated coloration. The genera are mostly founded on the dentition, which shows much diversity; the following are the principal:—_Myroconger_, _Enchelycore_, _Muraena_, _Thyrsoidea_, _Lycodontis_, _Pythonichthys_, _Echidna_, _Channomuraena_. The Muraena of the ancient Romans, _Muraena helena_, of the Mediterranean, Eastern Atlantic, and neighbouring parts of the Indian Ocean, occurring exceptionally as far north as the English coast, grows to 4 feet, and its flesh was more esteemed than that of any other Fish, large numbers being reared in specially constructed reservoirs near the sea, and fed on the corpses of slaves. _Channomuraena vittata_, from the coast of Cuba, is known to attain a length of 8 feet, and _Thyrsoidea macrura_, from the Indian Ocean and the Malay Archipelago, to upwards of 10 feet.

SUB-ORDER 5. HAPLOMI.

Air-bladder, if present, communicating with the digestive tract by a duct. Opercle well developed. Pectoral arch suspended from the skull; no mesocoracoid arch. Fins usually without, rarely with a few spines; ventrals abdominal, if present. Anterior vertebrae distinct, without Weberian ossicles.

The absence of the mesocoracoid arch distinguishes the Haplomi from the Malacopterygii, with which they are united by various authors. They lead to the Percesoces through the Cyprinodontids, and to the Lower Acanthopterygians, such as the Berycidae, through the Scopelids, Stephanoberycids, and Percopsids, as is evidenced by the structure of the mouth and the forward position, in some of the genera, of the ventral fins, which, however, are never attached to the pectoral girdle. Most of the forms which are here included inhabit either fresh water or the deep sea.

{606}SYNOPSIS OF THE FAMILIES.

I. Parietals separating the frontals from the supraoccipital; post-
temporal simple; praecaudal vertebrae with autogenous parapophyses.

Margin of the upper jaw formed by the praemaxillaries and the
maxillaries; basis cranii simple; no adipose dorsal fin
1. _Galaxiidae_.

Margin of the upper jaw formed by the praemaxillaries only; basis
cranii double; adipose dorsal fin present 2. _Haplochitonidae_.

II. Frontals in contact with the supraoccipital.

A. Praecaudal vertebrae without parapophyses.

1. Margin of the upper jaw formed by the praemaxillaries and the
maxillaries.

Body without or with minute scales, usually with rows of scutes;
adipose dorsal fin usually present 3. _Enchodontidae_.†

Body scaly; post-temporal forked; no adipose dorsal fin; ventrals
with 6 to 11 rays 4. _Esocidae_.

Body scaly; post-temporal incompletely ossified; pectoral fin
without pterygials; no adipose dorsal fin; ventrals with
3 rays only 5. _Dalliidae_.

2. Maxillaries excluded from the oral border.

a. Adipose dorsal fin usually present; ventral fin with 7 to
10 rays.

Post-temporal forked; dorsal fin formed of articulated rays
6. _Scopelidae_.

Post-temporal simple; dorsal fin very long, formed of slender,
non-articulated, simple or bifid rays 7. _Alepidosauridae_.

b. No adipose dorsal fin; head and mouth enormous, dentition
feeble; body naked; ventral fins, if present, with 5 rays
8. _Cetomimidae_.

B. Praecaudal vertebrae with well-developed parapophyses; maxillaries
excluded from the oral border.

1. Dorsal and anal fins without spines; scales cycloid, or with
erect spines; no adipose fin.

Mouth not protractile; ventral fins far forward, with 7 to
17 rays 9. _Chirothricidae_.†

Mouth not protractile; ventral fins remote from the pectorals,
with 9 rays 10. _Kneriidae_.

Mouth protractile; ventral fins, if present, with 5 to 7 rays
11. _Cyprinodontidae_.

Mouth scarcely protractile; ventral fins rudimentary or absent;
vent close to the gills 12. _Amblyopsidae_.

Mouth slightly protractile; ventral fins with 5 or 6 rays
13. _Stephanoberycidae_.

2. Dorsal and anal fins with true spines; scales ctenoid; an
adipose dorsal; ventral fins with 9 rays 14. _Percopsidae_.

† Fossil only.

{607}FAM. 1. GALAXIIDAE.—Margin of the upper jaw formed by the praemaxillaries and the maxillaries, the latter behind the former, and toothless. Parietals in contact with each other, and separating the frontals from the supraoccipital; opercular bones all well developed. Basis cranii simple. Ribs inserted on strong, autogenous parapophyses; epipleurals and epineurals. Post-temporal simple, attached to the epiotic; post-clavicle present. Body naked. Vertical fins far back; no adipose dorsal fin. Pectoral fins inserted very low down. Ventrals, if present, with seven rays. Air-bladder present. Ova falling into the cavity of the abdomen before exclusion.

The genus _Galaxias_ has an interesting distribution, the species of which it is made up occurring in the fresh waters of the southern hemisphere, viz. 8 in New Zealand and neighbouring islands, 7 in New South Wales, 3 or 4 in South Australia, 1 in West Australia, 2 in Tasmania, 7 in South America, from Chili southwards, and 1 at the Cape of Good Hope. One species (_G. attenuatus_) is even believed to be identical in New Zealand, Tasmania, South Australia, the Falkland Islands, and South America. This conclusion is probably correct from the fact, which may account for the distribution of the whole genus, {608}that it is not confined to fresh waters, but occurs also in the sea. Specimens were observed by Mr. Rupert Vallentin in the Falkland Islands, where the Fish is known to the inhabitants as "Smelts," in shoals in the shallow water along the shore; and, according to Mr. F. E. Clarke, the same species, in New Zealand, periodically descends to the sea, where it spawns, from January to March, and returns from March to May. A marine species has recently been discovered at the Chatham Islands. In New Zealand, the _Galaxias_ were called "Trout" by the settlers before the introduction of Salmonids, whilst the fry of _G. attenuatus_ are eaten as "Whitebait." The largest species reach the length of a foot. _Neochanna_, from New Zealand, differs from Galaxias in the absence of ventral fins; it has been found in burrows, which it excavates at a distance from water.

FAM. 2. HAPLOCHITONIDAE.—Small fresh-water Trout-like Fishes, agreeing in most respects with the Galaxiidae, to which they are unquestionably closely related, differing only in the greater extent of the praemaxillaries, which exclude the maxillary from the oral border, in the double basis cranii (the prootics uniting under the brain, leaving a canal between them and the parasphenoid), in the shorter parapophyses, which, like the neural arches of the praecaudal vertebrae, are autogenous, and in the presence of a small adipose dorsal fin, opposed to the anal.

Two genera: _Haplochiton_, naked, with a single species from Chili, the southern extremity of South America, and the Falkland Islands, and _Prototroctes_, covered with small scales, of which one species inhabits Queensland, another South Australia, and a third New Zealand. In _Haplochiton_, the urogenital orifice of both sexes is produced into a cylindrical tube, which lies concealed in a groove in front of the anal fin.

FAM. 3. ENCHODONTIDAE.—Margin of the upper jaw formed by the praemaxillaries and the maxillaries, the latter sometimes toothed like the former. Frontals in contact with the supraoccipital; basis cranii simple. Ribs sessile; praecaudal vertebrae without transverse processes. Rayed dorsal fin never much extended; sometimes an adipose fin behind it. Scales delicate or absent, but occasional longitudinal series of scutes occur, the dorsal series, when present, being unpaired.

Cretaceous Fishes allied to, and apparently more generalised than, the Esocidae and Scopelidae. Numerous remains from {609}Europe and North America, referred to 7 genera: _Enchodus_, _Eurypholis_, _Palaeolycus_, _Halec_, _Cimolichthys_, _Prionolepis_.

FAM. 4. ESOCIDAE.—Margin of the upper jaw formed by the praemaxillaries and maxillaries, the latter behind the former, and toothless. Supraoccipital in contact with the frontals, separating the small parietals; opercular bones all well developed; basis cranii simple. No parapophyses, except to the hindermost praecaudal vertebrae; epipleurals and epineurals. Post-temporal forked, the upper branch attached to the epiotic, the lower to the exoccipital; post-clavicle present. Vertical fins far back; no adipose dorsal fin. Pectoral fins inserted very low down; ventrals with 6 to 11 rays. Air-bladder present.

As in the Haplochitonidae, the neural and haemal arches are bones distinct from the centra, and although parapophyses are not developed, the ribs are not inserted on the centra, but on distinct bases wedged into the latter.[691] Teeth are present on the vomer, palatine, and pharyngeal bones.

A small family of carnivorous freshwater Fishes, including the Pike (_Esox_), of predaceous habits, unsurpassed in greediness and voracity, and the small and insignificant-looking _Umbra_, distinguished by the more anterior position of the dorsal fin, the larger scales, and the moderately large gape, with feeble villiform teeth. The range of the Esocidae is restricted to the cold and temperate parts of the northern hemisphere. Besides the well-known _Esox lucius_ of Europe, Northern Asia, and the northern parts of North America, growing to a length of 4 feet, and the Maskinongy (_E. nobilior_) of north-eastern North America, reaching twice that length, the first genus comprises three smaller species from the Eastern United States. Remains of _Esox_ have been found in {610}various freshwater deposits in Europe as far back as the Oligocene. _E. lepidotus_, of which very perfect specimens have been found in the Upper Miocene beds of Oeningen in Baden, differs from the living species in its much larger scales and in the greater approximation of the ventral and anal fins, two characters in which it approaches _Umbra_. Only two species of the latter are known: _U. crameri_ ("Hundsfisch"), from the stagnant waters of Austria-Hungary, and _U. limi_ ("Mud-Fish"), living in swamps and ditches in Canada and the north-eastern United States, often remaining imbedded in the mud of prairie sloughs and bog-holes.

FAM. 5. DALLIIDAE.—The genus _Dallia_, with a single species inhabiting the streams and ponds of Alaska and Siberia, is related to _Umbra_, but differs in the very thin and papery skeleton, with the post-temporal imperfectly ossified and the pectoral fin without pterygials or actinosts. The dorsal fin is far back and opposite to the anal, as in the Pike. The ventral fins are composed of three rays only, and the pectorals, which have a somewhat fleshy base, have as many as 36. The scales are extremely small, and partly imbedded in the skin. The Black-Fish, _D. pectoralis_, abounds in Sphagnum ponds, feeding on plants and worms, and forming the chief food of the natives of some parts of Northern Alaska, where, with the exception of the Salmonids, it is the only freshwater Fish. Turner, its discoverer, says its vitality is {611}extraordinary: Black-Fishes will remain frozen in baskets for weeks, and when thawed are as lively as ever, one having been swallowed in a congealed condition by a dog, thawed out by the heat of the stomach, and vomited up alive.

FAM. 6. SCOPELIDAE.—Praemaxillaries much elongate, and completely excluding the maxillaries from the oral border. Supraoccipital in contact with the frontals, sometimes partly covered by the parietals; opercular bones all well developed. Basis cranii simple. Ribs sessile; no parapophyses on the praecaudal vertebrae; epipleurals and epineurals. Post-temporal forked, the upper branch in contact with the epiotic or the supraoccipital, the lower with the opisthotic; post-clavicle present. An adipose dorsal fin often occurs; luminous spots often present on head and body. Ventral fins with 7 to 10 rays. Air-bladder sometimes absent.

A large family (over 100 known living species), mostly of pelagic and deep-sea Fishes. A great number of fossil types have been described.

Recent genera:

A. Without photophores: _Saurus_, _Saurida_, _Bathysaurus_, _Harpodon_, _Scopelarchus_, _Aulopus_, _Odontostomus_, _Omosudis_, _Sudis_, _Paralepis_, _Bathypterois_, _Benthosaurus_, _Chlorophthalmus_, _Ipnops_. B. With photophores: _Scopelus_, _Dasyscopelus_, _Neoscopelus_, _Scopelengys_, _Nannobrachium_, _Scopelosaurus_.

Fossil genera:

A. Cretaceous: _Sardinioides_, _Acrognathus_, _Leptosomus_, _Sardinius_, _Dactylopogon_, _Nematonotus_, _Microcoelia_, _Opisthopteryx_, _Apateodus_, _Rhinellus_. B. Eocene, Oligocene, and Miocene: _Omiodon_, _Scopeloides_, _Parascopelus_, _Anapterus_.

{612}

{613}The members of this Family vary much in form, and among them are to be found some of the most curious adaptations to bathybial existence. One of the best known is _Harpodon nehereus_, which, when newly taken, is brilliantly phosphorescent all over the body; in a salted and dry condition it is the "Bombay-duck," a delicacy eaten with curries, and exported in large quantities from the west coast of India. It is not known to occur at any great depth, and is not even restricted to the sea, being very abundant in the rivers and estuaries of Bengal and Burma; whilst an allied species, _H. squamosus_, is found in the Indian Ocean at depths of 120 to 300 fathoms. In _Bathypterois_, the eyes are very small; some of the rays of the paired fins being excessively prolonged, acting as tactile organs, and compensating the reduction in the eyes. Sir John Murray has observed about _B. longipes_: "When taken from the trawl [from 2650 fathoms] they were always dead, and the long pectoral rays were erected like an arch over the head, requiring considerable pressure to make them lie along the side of the body; when erected they resembled Pennatulids like _Umbellula_." In _Ipnops_, which resembles in general form the large-eyed _Chlorophthalmus gracilis_, the upper surface of the broad spatulate snout is occupied by a luminous organ longitudinally divided into two symmetrical halves, and the eyes are absent, unless, as first supposed, this extraordinary organ be a modification of them; but Professor Moseley's examination seems to have proved beyond doubt that it is a special form of phosphorescent organ, the object of which would be to attract other creatures to the wide gape of a Fish which, living in the abysses of the sea and deprived of organs of sight and touch, would have great difficulty in procuring its food. _Odontostomus_, with a very large eye which can be turned upwards and sidewards, and enormous compressed curved teeth, barbed at the tip and depressible backwards, is one of the few Scopelids in which scales are completely absent.

The numerous species (about 50) of _Scopelus_ and their allies are moderate-sized or small pelagic and deep-sea forms found in nearly all the seas, some coming to the surface at night, whilst others are confined to great depths; they are remarkable for the series of phosphorescent spots (photophores) on the body, and in some species also on the head, where they may form large patches on the snout. The arrangement of these photophores is a very {614}definite one, and it has been used for the division of these Fishes into genera or sub-genera.[692] The ventral fins have a more forward position than in most other members of the Family.

FAM. 7. ALEPIDOSAURIDAE.—Characters as in the preceding, but supratemporal simple, attached to the opisthotic, and dorsal fin very long, formed of slender, non-articulated, simple or bifid rays, extending along nearly the whole length of the back, followed by a small adipose fin. The air-bladder is absent and the body scaleless. The skeleton is feebly ossified; the dentition is very powerful, some of the teeth on the palate and mandible being very strongly enlarged. 4 or 5 species are known, from considerable depths in the Atlantic and Pacific Oceans, referable to one genus, _Alepidosaurus_ or _Plagyodus_. _A. ferox_, from the Atlantic, reaches a length of 4 feet.

FAM. 8. CETOMIMIDAE.—The affinities of the recently discovered genera _Rondeletia_ and _Cetomimus_, deep-sea Fishes from the North Atlantic, at depths of 1000 to 1600 fathoms, are still uncertain, as the skeleton could not be examined; they are probably most nearly related to the Scopelidae. The head is enormous, with very wide gape, that of _Cetomimus_ being suggestive of that of a Right Whale; the teeth are small and coarsely granular; the gill-openings are very wide; the body is more or less compressed and scaleless; the dorsal and anal fins are opposed to each other; no adipose dorsal fin. In _Rondeletia_, the eyes are moderately large, and ventral fins, with 5 rays, are present; in _Cetomimus_, the eyes are very small, and ventral fins are absent.

{615}FAM. 9. CHIROTHRICIDAE.—Praemaxillaries delicate and styliform, completely excluding the maxillaries from the upper border of the mouth; jaws with feeble dentition or toothless; opercular apparatus complete. Praecaudal vertebrae with robust parapophyses, to which ribs are attached. Ventral fins far forwards.

These Fishes, of which three fossil genera are known from the Cretaceous of Germany and Syria, appear to be related to the Scopelidae, from which the strong parapophyses distinguish them. _Chirothrix_ is remarkable for its excessively enlarged ventral fins with about 17 rays; these fins were taken for the pectorals by the early describers. In _Telepholis_ and _Exocoetoides_, the ventral fins are smaller than the pectorals, and formed of 7 or 8 rays only; the dorsal region, in the former, is protected by a covering of small, thin, rounded or polygonal dermal scutes, each bearing a median tubercle.

FAM. 10. KNERIIDAE.—Margin of the upper jaw formed by the praemaxillaries; mouth toothless, not protractile. Parietals separated by the supraoccipital. Pharyngeal bones toothless. Praecaudal vertebrae with parapophyses. Body covered with small scales. Ventrals with 9 rays. No adipose dorsal fin. Air-bladder present.

{616}The genus _Kneria_ comprises two species from the fresh waters of tropical Africa, one from Angola, the other from East Africa.[693] Small Loach-like Fishes, two to four inches long, with the upper jaw projecting beyond the mouth, which is inferior and transverse; no barbels; gill-membranes entirely grown to the isthmus, the gill-opening being a rather narrow vertical slit; dorsal and anal fins short, the former opposite, or nearly opposite, to the ventrals; the snout of the male(?) of _K. angolensis_ is described as beset with small spine-like excrescences; the intestinal tract makes several convolutions.

FAM. 11. CYPRINODONTIDAE.—Mouth protractile, the maxillaries excluded from the oral border; teeth in the jaws and on the pharyngeal bones; pterygo-palatine arch weak or rudimentary; opercular bones all well developed. Basis cranii simple. Praecaudal vertebrae with strong parapophyses, bearing the ribs; epipleurals inserted on the ribs. Post-temporal forked. Ventrals, if present, with 5 to 7 rays. No adipose dorsal fin. Air-bladder sometimes absent.

From a physiological point of view, this Family may be divided into carnivorous forms, with short digestive tract, and phytophagous or limnophagous ones, in which the intestine forms numerous coils. To the first division belong the living genera _Cyprinodon_, _Characodon_, _Tellia_, _Haplochilus_, _Fundulus_, _Rivulus_, _Cynolebias_, _Orestias_, _Empetrichthys_, _Jenynsia_, _Pseudoxiphophorus_, _Belonesox_, _Gambusia_, _Anableps_, among existing forms, and the fossil genera _Prolebias_ (Oligocene and Miocene) and _Pachylebias_ (Miocene); to the second, the living genera _Poecilia_, _Mollienesia_, _Platypoecilus_, and _Girardinus_. _Procatopus_, a near ally of _Haplochilus_, recently discovered in South Cameroon, is remarkable for having the ventral fins inserted far forward, below the pectoral fins.

These are small or very small Fishes,[694] only a few reaching a length of about a foot, confined to fresh or brackish waters, recognisable externally by the flat head with protractile mouth, the usually large scales, and the absence of a well-developed lateral {617}line. The teeth vary much in shape: cardiform, villiform, or compressed, and bi- or tri-cuspid; the palate is either toothless, or teeth are present on the vomer. About 200 species are known, mostly from the American continent, only about 30 being known from other parts of the world, viz. Southern Europe, Southern Asia and Japan, and Africa. In many species the sexes are dissimilar, the female being larger and less brilliantly coloured, with smaller fins; the anal fin of the male may be modified into an intromittent organ by means of which internal fertilisation takes place, the ova developing in a sort of uterus, which the young leave in a more or less advanced stage of growth. The most curious of the Cyprinodontids is the genus _Anableps_, of Central and South America, surface-swimming Fishes, the strongly projecting eyes of which are divided by a horizontal band of the conjunctiva into an upper part adapted for vision in the air, and a lower for vision in the water, and the pupil is divided into two parts by a constriction; the larger species grows to the length of a foot.

{618}FAM. 12. AMBLYOPSIDAE.—Mouth scarcely protractile, the maxillaries excluded from the oral border; teeth small, in jaws and palate, and on the pharyngeal bones. Praecaudal vertebrae with very strong parapophyses, bearing the ribs on their upper surface; epipleurals inserted on the ribs. Ventral fins rudimentary or absent. Vent jugular, close to the gill-clefts. Air-bladder present.

Small ovoviviparous Fishes, closely related to, and evidently derived from, the Cyprinodontids, measuring from 1 to 5 inches, inhabiting ditches and small streams, or confined to subterranean waters of limestone caves, in the United States east of the Rocky Mountains. Six species, referable to three genera, are known. In _Chologaster_, the eyes are well developed and the body is coloured. _C. cornutus_ inhabits the lowland streams and swamps of the South Atlantic States, from Virginia to Florida; _C. agassizii_ is found in the underground streams of Kentucky and Tennessee; and _C. papilliferus_ occurs under stones in the springs of south-western Illinois. _Amblyopsis_ and _Typhlichthys_, which are evidently derived from the former, or from forms closely related to it, have the eyes rudimentary and more or less concealed under the skin, and the body is colourless. _Amblyopsis spelaea_ is widely distributed in the caves east of the Mississippi, {619}both north and south of the Ohio River; it is common in the River Styx of the Mammoth Cave. _Typhlichthys subterraneus_ is found with the latter species in the caves east of the Mississippi, but is confined to the south side of the Ohio River, whilst _T_. (_Troglichthys_) _rosae_ is found in the caves west of the Mississippi River. Of _Amblyopsis spelaea_, the late Professor Cope has observed: "If these Amblyopses be not alarmed, they come to the surface to feed, and swim in full sight, like white aquatic ghosts. They are then easily taken by the hand or net, if perfect silence is preserved, for they are unconscious of the presence of an enemy except through the medium of hearing; this sense, however, is evidently very acute, for at any noise they turn suddenly downwards, and hide beneath stones, etc., on the bottom." Dr. Garman thinks, on the contrary, that such a sense can hardly be developed in recesses where we are accustomed to think any sounds other than those made by the rippling or dripping water are almost unknown, and that it is through the sense of touch, and not through hearing, that the Fish is disturbed. In fact, the head is provided with a great number of tactile papillae, arranged in transverse ridges, provided with nervous filaments, which evidently compensate the loss of the visual organ.[695]

FAM. 13. STEPHANOBERYCIDAE.—This Family has hitherto been placed near the Berycidae, among the Acanthopterygii, but there are no spinous rays in the dorsal and anal fins; and the ventrals, formed of one simple and four or five branched rays, are abdominal. The genus _Stephanoberyx_, with two species from the Atlantic, at depths of 535 to 2949 fathoms, is characterised by a large, thick, cavernous head, with thin bony spine-bearing ridges, a large mouth bordered by the protractile praemaxillaries, behind which are the large maxillaries, a short dorsal and a short anal, opposed to each other behind the ventrals, and the body covered with feebly imbricated scales, each bearing in the centre one or several erect spines. The largest specimen measures 6 inches. _Malacosarcus_, a small Fish from the Pacific, at depths of 2350 and 2425 fathoms, is very closely allied to _Stephanoberyx_, but its scales are very thin and cycloid. The striking resemblance which the head {620}bears to that of the Berycid _Melamphaes_ may be merely a case of convergence, and it must be borne in mind that this appearance is approached by some species of _Scopelus_, with which both _Malacosarcus_ and _Melamphaes_ were originally confounded. The praecaudal vertebrae are provided with parapophyses. I have ascertained on a specimen of _Stephanoberyx monae_ that the air-bladder is connected with the dorsal side of the stomach by a short and comparatively wide duct.

FAM. 14. PERCOPSIDAE.—Margin of the upper jaw formed by the praemaxillaries; mouth small, not protractile, toothed; palate toothless. Supraoccipital in contact with the frontals, separating the small parietals. Basis cranii simple. Most of the praecaudal vertebrae with parapophyses, on the upper surface of which the ribs are inserted; no epipleurals. Post-temporal forked; post-clavicle present; scapular foramen in the scapula, on which three hour-glass-shaped pterygials are inserted, a fourth being inserted on the coracoid. Dorsal fin with two true spines; anal with one or two; ventrals far forward, with 9 rays; pectorals inserted rather high. A small adipose dorsal fin. Body covered with strongly ctenoid scales. Air-bladder present (with open duct).

This is a most interesting group of Fishes, from the resemblance which they bear to the Perches, and they have therefore been raised to the rank of a sub-order, Salmopercae, by Jordan and Evermann, who regard them as "archaic fishes, relics of some earlier fauna, and apparently derived directly from the extinct transitional forms through which the Haplomi and Acanthopteri have descended from allies of the Isospondyli [Malacopterygii]." On the other hand, an analysis of their characters shows them to belong to the Haplomi, of which they {621}may be regarded as highly specialised members, having evolved in the direction of the Acanthopterygii.

Only two genera are known, each with a single species: _Percopsis_, from the rivers and streams of Canada and the north-eastern United States, and _Columbia_, more recently discovered in the sandy or weedy lagoons along the Columbia River. These Fishes are of small size, not exceeding 6 inches in length. Their eggs are unusually large.

SUB-ORDER 6. HETEROMI.

Air-bladder without open duct. Opercle well developed; parietal bones separating the frontals from the supraoccipital. Pectoral arch suspended from the supraoccipital or the epiotic, the post-temporal small and simple or replaced by a ligament; no mesocoracoid. Ventral fins abdominal, if present.

The Halosauridae and Notacanthidae are deep-sea Fishes of obscure affinities. In the abdominal position of the many-rayed ventral fins and in the absence of the mesocoracoid arch they agree with the Haplomi; but if, as the investigations of Günther lead us to believe,[696] there is really no open communication between the air-bladder and the digestive tract, they {622}should be removed from this physostomous sub-order. The two families have many characters in common, such as the attachment and structure of the pectoral arch, which is devoid of a post-clavicle, the position of the pectoral fins high up the sides, the strong parapophyses inserted very low down on the centra of the vertebrae, the extent of the parietal bones, which meet in a sagittal suture and separate the frontals from the supraoccipital. The recent discovery of a third family, the Lipogenyidae, which, in the structure of the dorsal fin, is exactly intermediate between the two others, has lessened the gap between the Lyomeri (Halosauridae) and Heteromi (Notacanthidae) of Gill, which I have proposed to unite in a suborder under the latter name.

These Fishes are no doubt derived from forms in which a separate caudal fin existed; such a type must have been near the Dercetidae, as defined by A. S. Woodward, which may provisionally be placed here.

An imperfectly known Fish from the Chalk of Mount Lebanon, _Pronotacanthus sahelalmae_, appears to bear some affinity to _Notacanthus_, and has been placed in the same family; but its characters are not sufficiently defined to refer it without doubt to this division.

There is a fifth family which may enter this sub-order: the Fierasferidae, the structure of which has been exquisitely described and figured by Emery.[697] Hitherto placed with or near the Ophidiidae, they differ widely from them, as well as from all Acanthopterygians, in the conformation of the skull, the supraoccipital being separated from the frontals by the parietals, which form a long median suture. This is a feature which has only been observed in Fishes with abdominal ventral fins, and although the total absence of those fins in _Fierasfer_ deprive us of an important criterion in deciding on its affinities, I am inclined to regard this family as derived from an "abdominal" type. The conformation of the pectoral arch has much in common with that of the Halosaurs, and, notwithstanding the interpretation that has been given to the bones at the back of {623}the cranium in the latter type, the same may be said, in a general way, of the skull.

As pointed out by Emery, the very anterior position of the vent in the Fierasferidae is directly related to the curious mode of life of these Fishes, and the analogous condition obtained in various families, such as the Gymnotidae, Nemichthyidae, Amblyopsidae, shows it to be a character of relatively small systematic importance.

SYNOPSIS OF THE FAMILIES.

A. Vent posterior.

_a_. A distinct caudal fin; ordinary scales small or wanting, but
enlarged scutes along the side 1. _Dercetidae_.†

_b_. Tail tapering to a point; scales cycloid.

No spines; dorsal fin short, anal very long 2. _Halosauridae_.

Fins with spines, dorsal short, anal long 3. _Lipogenyidae_.

Dorsal fin formed of a series of spines, anal long, formed partly
of spines and partly of soft rays 4. _Notacanthidae_.

B. Vent immediately behind the gill-opening; no caudal fin; scales
absent 5. _Fierasferidae_.

FAM. 1. DERCETIDAE.—Body much elongate; ordinary scales small or wanting, but two or more continuous series of enlarged scutes along each side; mouth large, praemaxillaries apparently forming the greater part of the upper border of the mouth, which is toothed; opercular apparatus complete. Dorsal fin more or less extended, without spines; anal short, caudal separate; ventrals with not less than 7 or 8 rays.

_Dercetis_, _Leptotrachelus_, _Leptecodon_, _Pelargorhynchus_, and _Stratodus_, from the Upper Cretaceous of Europe, Syria, and North America.