Chapter XXXVI: Part V: , Washington, 1879, 8vo

8. _C. sapidissima._--The American Shad, abundant, and an important food-fish on the Atlantic coasts of North America. Spawns in fresh water.

9. _C. mattowocca._--The “Gaspereau” or “Ale-wife,” common on the Atlantic coasts of North America, ascending into freshwater in early spring, and spawning in ponds and lakes.

10. _C. pilchardus._--The “Pilchard” or the “Sardine,” equally abundant in the British Channel, on the coast of Portugal, and in the Mediterranean, and readily recognised by radiating ridges on the operculum, descending towards the sub-operculum.

11. _C. sagax._--Representing the Pilchard in the Pacific, and found in equally large shoals on the coasts of California, Chile, New Zealand, and Japan.

12. _C. toli._--The subject of a very extensive fishery on the coast of Sumatra for the sake of its roes, which are salted and exported to China, the dried fish themselves being sent into the interior of the island. The fish is called “Trubu” by the Malays, about 18 inches long, and it is said that between fourteen and fifteen millions are caught annually.

13. _C. scombrina._--The “Oil-Sardine” of the eastern coast of the Indian Peninsula.

* * * * *

Other, but less important genera of Clupeoids with serrated abdomen, are _Clupeoides_, _Pellonula_, _Clupeichthys_, _Pellona_, _Pristigaster_, and _Chirocentrodon_ (these three last with very small or without any ventral fins).

ALBULA.--Body oblong, moderately compressed; abdomen flat.
Scales of moderate size, adherent; lateral line distinct. Eyes
covered with a broad annular adipose membrane. Snout pointed,
the upper jaw projecting beyond the lower. Mouth inferior, of
moderate width, with villiform teeth; intermaxillary juxtaposed
to the upper anterior edge of the maxillary. Dorsal fin opposite
to the ventrals; anal fin shorter than dorsal. Gill-membranes
entirely separate, with numerous branchiostegals.

One species only (_A. conorhynchus_), ranging over all tropical and sub-tropical seas, and very common in many localities near the coasts. It grows to a length of from two to three feet, and is not valued as food.

ELOPS.--Body rather elongate, moderately compressed; abdomen
flat. Scales small, adherent; lateral line distinct. A narrow
osseous lamella, attached to the mandibulary symphysis, covers
the part between the mandibles. Snout pointed; mouth wide,
anterior; intermaxillary short, maxillary forming the lateral
part of the mouth. Bands of villiform teeth in the jaws, on the
vomer, palatine and pterygoid bones, on the tongue, and on the
base of the skull. Dorsal fin opposite to ventrals; anal rather
shorter than dorsal. Gill-membranes entirely separate, with very
numerous branchiostegals.

Two species, of which one, _E. saurus_, is, like the preceding fish, spread over all tropical and sub-tropical seas; it exceeds a length of three feet, and is not esteemed as food.

MEGALOPS.--Body oblong, compressed, abdomen flat. Scales large,
adherent; lateral line distinct. A narrow osseous lamella,
attached to the mandibulary symphysis, between the mandibles.
Snout obtusely conical; mouth anterior, lower jaw prominent;
intermaxillary short; maxillary forming the lateral part of
the mouth. Bands of villiform teeth in the jaws, on the vomer,
palatine and pterygoid bones, on the tongue and on the base
of the skull. Dorsal fin opposite to, or immediately behind,
the ventrals; anal rather larger than dorsal. Gill-membranes
entirely separate, with numerous branchiostegals. Pseudobranchiæ
none.

Two species, one belonging to the Indo-Pacific (_M. cyprinoides_), the other to the Atlantic (_M. thrissoides_); they are the largest fishes of this family, exceeding a length of five feet, and excellent eating. Young specimens enter freely fresh waters.

CHANOS.--Body oblong, compressed; abdomen flat. Scales small,
striated, adherent; lateral line distinct. Snout depressed;
mouth small, anterior, transverse, the lower jaw with a small
symphysial tubercle. Intermaxillary in juxtaposition to the
upper anterior edge of maxillary. Teeth none. Dorsal fin
opposite to the ventrals; anal small, shorter than dorsal;
caudal deeply forked. Gill-membranes entirely united below, and
free from the isthmus. Branchiostegals four, long. An accessory
branchial organ in a cavity behind the gill-cavity proper.
Air-bladder divided by a constriction into an anterior and
posterior portion. Mucous membrane of the œsophagus raised in a
spiral fold. Intestine with many convolutions.

Two species from the Indo-Pacific, of which _Ch. salmoneus_ is extremely common; it enters fresh waters, and exceeds a length of four feet; its flesh is highly esteemed. The accessory branchial organ and the skeleton have been described by _Müller_, “Bau und Grenzen der Ganoiden,” p. 75; and by _Hyrtl_, “Denkschr. Ak. Wiss. Wien.” xxi. 1883, p. 1.

* * * * *

The remaining genera belonging to this family are _Spratelloides_, _Dussumieria_, and _Etrumeus_, which together form a small group, distinguished by an anterior and lateral mouth, by the upper jaw not overlapping the lower, by a rounded abdomen, and by lacking the gular plate of some of the preceding genera.

TWENTY-THIRD FAMILY--BATHYTHRISSIDÆ.

_Body oblong, with rounded abdomen, covered with cycloid scales; head naked; barbels none. Margin of the upper jaw formed by the intermaxillaries mesially, and by the maxillaries laterally. Opercular apparatus complete. Adipose fin none; dorsal fin much elongate, many rayed; anal fin short. Stomach with a blind sac; pyloric appendages numerous. Gill-apparatus well developed; pseudobranchiæ; gill-openings wide; an air-bladder. Ova very small; ovaries without duct._

One genus and species only (_Bathythrissa dorsalis_) from deep water (350 fathoms) off the coast of Japan. This remarkable fish has the appearance of a _Coregonus_, and attains to a length of two feet. Nothing is known of its osteology, but possibly a fossil genus from the Gyps of Montmartre; _Notæus_, which has also a long dorsal fin, may prove to belong to the same family.

TWENTY-FOURTH FAMILY--CHIROCENTRIDÆ.

_Body covered with thin, deciduous scales; barbels none. Margin of the upper jaw formed by the intermaxillaries mesially, and by the maxillaries laterally, both bones being firmly united, in juxtaposition. Opercular apparatus complete. Adipose fin none; the dorsal fin belongs to the caudal portion of the vertebral column. Stomach with a blind sac; intestine short, the mucous membrane forming a spiral fold; pyloric appendages none. Pseudobranchiæ none; air-bladder incompletely divided into cells; gill-opening wide._

One genus and species only (_Chirocentrus dorab_) is known, which is common in the Indian Ocean, and attains to a length of about three feet; it is not esteemed as food. Remains of fishes similar to _Chirocentrus_ are found in the marl slates of Padang, in Sumatra.

TWENTY-FIFTH FAMILY--ALEPOCEPHALIDÆ.

_Body with or without scales; head naked; barbels none. Margin of the upper jaw formed by the intermaxillaries and maxillaries, the former being placed along the upper anterior edge of the latter. Opercular apparatus complete. Adipose fin none; the dorsal fin belongs to the caudal portion of the vertebral column. Stomach curved, without blind sac; pyloric appendages in moderate number. Pseudobranchiæ; air-bladder absent. Gill-openings very wide._

Before the voyage of the “Challenger” one species only of this family was known, _Alepocephalus rostratus_, a rare fish from the Mediterranean; now, four genera with seven species are known, and there is no doubt that this family is one of the most characteristic, and will prove to be one of the most generally distributed forms, of the deep-sea. Their vertical range varies between 345 (_Xenodermichthys_) and 2150 (_Bathytroctes_) fathoms. They approach the Salmonoids, but lack invariably the adipose fin. Their dentition is very feeble; their eye large; bones thin. Coloration black.

ALEPOCEPHALUS has thin cycloid scales; a mouth of moderate
width, and no teeth on the maxillary.

BATHYTROCTES has cycloid scales, a wide mouth, and teeth on the
maxillary as well as intermaxillary.

PLATYTROCTES has small keeled scales and no ventrals.

XENODERMICHTHYS with fine nodules instead of scales.

TWENTY-SIXTH FAMILY--NOTOPTERIDÆ.

_Head and body scaly; barbels none. Margin of the upper jaw formed by the intermaxillaries mesially, and by the maxillaries laterally. Opercular apparatus incomplete. Tail prolonged, tapering. Adipose fin none. Dorsal short, belonging to the caudal portion of the vertebral column; anal very long. Stomach without blind sac; two pyloric appendages. Pseudo__branchiae none; air-bladder present, divided in the interior. The ova fall into the cavity of the abdomen before exclusion. On each side a parieto-mastoid cavity leading into the interior of the skull._

One genus only (_Notopterus_) with five species which inhabit fresh waters of the East Indies and West Africa. Well-preserved remains of this genus occur in the marl slates of Padang, in Sumatra. Their air-bladder is divided into several compartments, and terminates in two horns anteriorly and posteriorly, the anterior horns being in direct connection with the auditory organ.

TWENTY-SEVENTH FAMILY--HALOSAURIDÆ.

_Body covered with cycloid scales; head scaly; barbels none. Margin of the upper jaw formed by the intermaxillaries mesially, and by the maxillaries laterally. Opercular apparatus incomplete. Adipose fin none. The short dorsal belongs to the abdominal part of the vertebral column; anal very long. Stomach with a blind sac; intestine short; pyloric appendages in moderate number. Pseudobranchiæ none. Air-bladder large, simple; gill-openings wide. Ovaries closed._

The only genus belonging to this family was discovered by the Madeiran ichthyologist Johnson, in 1863; but since then the naturalists of the “Challenger” expedition have added four other species, showing that this type is a deep-sea form and widely distributed; the specimens were dredged in depths varying from 560 to 2750 fathoms.

TWENTY-EIGHTH FAMILY--HOPLOPLEURIDÆ.

_Body generally with four series of subtriangular scutes, and with intermediate scale-like smaller ones. One (?) dorsal only; head long, with the jaws produced._

_Extinct_; developed in the chalk and extending into tertiary formations: _Dercetis_ (with the upper jaw longest), _Leptotrachelus_, _Pelargorhynchus_, _Plinthophorus_, _Saurorhamphus_ (with the lower jaw longest), _Eurypholis_; _Ischyrocephalus_ (?). The latter genus, from cretaceous formations of Westphalia, is said to have two dorsal fins.

TWENTY-NINTH FAMILY--GYMNOTIDÆ.

_Head scaleless; barbels none. Body elongate, eel-shaped. Margin of the upper jaw formed in the middle by the intermaxillaries, and laterally by the maxillaries. Dorsal fin absent or reduced to an adipose strip; caudal generally absent, the tail terminating in a point. Anal fin exceedingly long. Ventrals none. Extremity of the tapering tail capable of being reproduced. Vent situated at, or at a short distance behind, the throat. Humeral arch attached to the skull. Ribs well developed. Gill-openings rather narrow. Air-bladder present, double. Stomach with a cæcal sac and pyloric appendages. Ovaries with oviducts._

Eel-like freshwater fishes from Tropical America.

STERNARCHUS.--Tail terminating in a distinct small caudal fin.
Teeth small. A rudimentary dorsal fin is indicated by an adipose
band fitting into a groove on the back of the tail; it is easily
detached, so as to appear as a thong-like appendage fixed in
front. Branchiostegals four.

Eight species, some have the snout compressed and of moderate length, like _St. Bonapartii_ from the River Amazons; others have it produced into a long tube, as St. oxyrhynchus from the Essequibo.

RHAMPHICHTHYS.--Caudal fin none; teeth none; no trace of a
dorsal fin. No free orbital margin.

Six species, of which, again, some have a tubiform snout, whilst in the others it is short.

STERNOPYGUS.--Caudal fin none; no trace of a dorsal fin. Both
jaws with small villiform teeth; similar teeth on each side of
the palate. Body scaly.

Four species, very common, and growing to a length of 30 inches.

CARAPUS.--Caudal fin none; no trace of a dorsal fin. A series of
conical teeth in each jaw. Anterior nostrils, wide in the upper
lip. Body scaly.

One species (_C. fasciatus_) extremely common, and found all over tropical America, east of the Andes, from 18 to 24 inches long.

GYMNOTUS.--Caudal and dorsal fins absent; anal extending to the
end of the tail. Scales none. Teeth conical, in a single series.
Eyes exceedingly small.

The “Electric Eel” is the most powerful of electric fishes, growing to a length of six feet, and extremely abundant in certain localities of Brazil and the Guyanas. The electric organ consists of two pairs of longitudinal bodies, situated immediately below the skin, above the muscles; one pair on the back of the tail, and the other pair along the anal fin. Each fasciculus is composed of flat partitions or septa, with transverse divisions between them. The outer edge of the septa appear in nearly parallel lines in the direction of the longitudinal axis of the body, and consist of thin membranes, which are easily torn; they serve the same purpose as the columns in the analogous organ of the Torpedo, making the walls or abutments for the perpendicular and transverse dissepiments, which are exceedingly numerous, and so closely aggregated as to seem almost in contact. The minute prismatic cells, intercepted between these two sorts of plates, contain a gelatinous matter; the septa are about one-thirtieth of an inch from each other, and one inch in length contains a series of 240 cells, giving an enormous surface to the electric organs. The whole apparatus is supplied with more than 200 nerves, which are the continuations of the rami anteriores of the spinal nerves. In their course they give out branches to the muscles of the back, and to the skin of the animal. In the Gymnotus, as in the Torpedo, the nerves supplying the electric organs are much larger than those bestowed on any part for the purposes of sensation or movement.

The graphic description by Humboldt of the capture of Electric Eels by horses driven into the water, which would receive the electric discharges and thus exhaust the fishes, seems to rest either on the imagination of some person who told it to the great traveller or on some isolated incident. Recent travellers have not been able to verify it even in the same parts of the country where the practice was said to exist.

THIRTIETH FAMILY--SYMBRANCHIDÆ.

_Body elongate, naked or covered with minute scales; barbels none. Margin of the upper jaw formed by the intermaxillaries only, the well developed maxillaries lying behind and parallel to them. Paired fins none. Vertical fins rudimentary, reduced to more or less distinct cutaneous folds. Vent situated at a, great distance behind the head. Ribs present. Gill-openings confluent into one slit situated on the ventral surface. Air-bladder none. Stomach without cæcal sac or pyloric appendages. Ovaries with oviducts._

The fishes of this family consist of freshwater-fishes from tropical America and Asia, which, however, enter also brackish water; and of a truly marine genus from Australia.

AMPHIPNOUS.--Vent in the posterior half of the body, which is
covered with minute scales longitudinally arranged.

A common fish (_A. cuchia_) in Bengal, remarkable for its singular respiratory apparatus. It has only three branchial arches, with rudimentary branchial laminæ, and with very narrow slits between the arches. To supplement this insufficient respiratory apparatus, a lung-like sac is developed on each side of the body behind the head, opening between the hyoid and first branchial arch. The interior of the sac is abundantly provided with blood-vessels, the arterial coming from the branchial arteries, whilst those issuing from it unite to form the aorta. _A. cuchia_ approaches the Eels in having the humeral arch not attached to the skull.

MONOPTERUS.--Vent in the posterior half of the body, which
is naked. Three branchial arches with rudimentary gills, but
without breathing sac.

One species (_M. javanicus_), which is extremely common in the East Indian Archipelago and in the eastern parts of the Continent. Upwards of three feet long.

SYMBRANCHUS.--Vent in the posterior half of the body, which is
naked. Four branchial arches with well developed gills.

Three species, of which one (_S. marmoratus_) is extremely common in tropical America, and the other (_S. bengalensis_) not less so in the East Indies.

CHILOBRANCHUS.--Vent in the anterior half of the length of
the body, which is naked. Vertical fins reduced to a simple
cutaneous fold, without rays.

A small fish (_Ch. dorsalis_) from North Western Australia and Tasmania.

THIRTY-FIRST FAMILY--MURÆNIDÆ.

_Body elongate, cylindrical or “band-shaped, naked or with rudimentary scales. Vent situated at a great distance from the head. Ventral fins none. Vertical fins, if present, confluent, or separated by the projecting tip of the tail. Sides of the upper jaw formed by the tooth-bearing maxillaries, the fore part by the intermaxillary, which is more or less coalescent with the vomer and ethmoid. Humeral arch not attached to the skull. Stomach with a blind sac; no pyloric appendages. Organs of reproduction without efferent ducts._

The “Eels” are spread over almost all fresh waters and seas of the temperate and tropical zones; some descend to the greatest depths of the oceans. The young of some have a limited pelagic existence. (_Leptocephali_, see p. 179.) At Monte Bolca fossil remains are very numerous, belonging to recent genera, _Anguilla_, _Sphagebranchus_, and _Ophichthys_; even larval Leptocephales have been preserved. _Anguilla_ has been found also in the chalk of Aix and Oeningen.

In the majority of the species the branchial openings in the pharynx are wide slits (_Murænidæ platyschistæ_); in others, the true Murænæ, (_Murænidæ engyschistæ_) they are narrow.

NEMICHTHYS.--Exceedingly elongate, band-shaped; tail tapering
into a point. Vent approximate to the pectorals, but the
abdominal cavity extending far behind the vent. Jaws produced
into a long slender bill, the upper part being formed by the
vomer and intermaxillaries. The inner surface of the bill
covered with small tooth-like asperities. Eye large. The
nostrils of each side are close together, in a hollow before the
eye. Gill-openings wide, nearly confluent. Pectoral and vertical
fins well developed.

This very singular type is a deep-sea form, occurring at depths of from 500 to 2500 fathoms. The two species known have hitherto been found in the Atlantic only.

CYEMA.--This genus combines the form of the snout of
_Nemichthys_, with the soft and shorter body of a
_Leptocephalus_; but the gill-openings are very narrow and close
together on the abdominal surface. Vent in about the middle of
the length of the body; vertical fins well developed, confined
to, and surrounding, the tail. Pectoral fins well developed. Eye
very small.

Known from two specimens only, 4½ inches long, dredged in depths of 1500 and 1800 fathoms in the Pacific and Antarctic Oceans.

SACCOPHARYNX.--Deep-sea Congers, with the muscular system
very feebly developed, with the bones very thin, soft, and
wanting in inorganic matter. Head and gape enormous. Snout
very short, pointed, flexible, like an appendage overlapping
the gape. Maxillary and mandibulary bones very thin, slender,
arched, armed with one or two series of long, slender, curved,
widely set teeth, their points being directed inwards; palate
toothless. Gill-openings wide, at some distance from the head,
at the lower part of the sides; gills very narrow, free, and
exposed. Trunk of moderate length. Stomach distensible in
an extraordinary degree. Vent at the end of the trunk. Tail
band-like, exceedingly long, tapering in a very fine filament.
Pectoral small, present. Dorsal and anal fins rudimentary.

This is another extraordinary form of Deep-sea Eels; the muscular system, except on the head, is very feebly developed; the bones are as thin, soft, and wanting in inorganic matter, as in the _Trachypteridæ_. This fish is known from three specimens only, which have been found floating on the surface of the North Atlantic, with their stomachs much distended, having swallowed some other fish, the weight of which many times exceeded that of their destroyer. It attains to the length of several feet.

SYNAPHOBRANCHUS.--Gill-openings ventral, united into a
longitudinal slit between the pectoral fins, separate
internally. Pectoral and vertical fins well developed. Nostrils
lateral, the anterior subtubular, the posterior round, before
the lower half of the eye. Cleft of the mouth very wide; teeth
small; body scaly. Stomach very distensible.

Deep-sea Congers, with well-developed muscular system, spread over all oceans, and occurring in depths of from 345 to 2000 fathoms. Four species are known. Probably attaining to the same length as the Conger.

ANGUILLA.--Small scales imbedded in the skin. Upper jaw not
projecting beyond the lower. Teeth small, forming bands.
Gill-openings narrow, at the base of the pectoral fins. The
dorsal fin commences at a considerable distance from the occiput.

Some twenty-five species of “Eels” are known from the freshwaters and coasts of the temperate and tropical zones; none have been found in South America or the west coast of North America and West Africa. The following are the most noteworthy:--The common European species (_A. anguilla_) is spread over Europe to 64° 30´ lat. N., and all round the Mediterranean area, but is not found either in the Danube or in the Black and Caspian Seas; it extends across the Atlantic to North America. The form of the snout varies much, and some naturalists have believed that specimens with a broad and obtuse snout were specifically distinct from those with pointed snout. However, every degree of breadth of the snout may be observed; and a much safer way of recognizing this species, and distinguishing it from other European Eels, is the forward position of the dorsal fin; the distance between the commencement of the dorsal and anal fins being as long as, or somewhat longer than, the head. Eels grow generally to a length of about three feet, but the capture of much larger examples is on record. Their mode of propagation is still unknown. So much only is certain that they do not spawn in fresh water, that many full-grown individuals, but not all, descend rivers during the winter months, and that some of them at least must spawn in brackish water or in deep water in the sea; for in the course of the summer young individuals from three to five inches long ascend rivers in incredible numbers, overcoming all obstacles, ascending vertical walls or floodgates, entering every larger and smaller tributary, and making their way even over terra firma to waters shut off from all communication with rivers. Such immigrations have been long known by the name of “_Eel-fairs_.” The majority of the Eels which migrate to the sea appear to return to fresh water, but not in a body, but irregularly, and throughout the warmer part of the year. No naturalist has ever observed these fishes in the act of spawning, or found mature ova; and the organs of reproduction of individuals caught in fresh water are so little developed and so much alike, that the female organ can be distinguished from the male only with the aid of a microscope.

The second species found in Great Britain, on the coasts of Europe generally, in China, New Zealand, and the West Indies, is (_A. latirostris_) the “Grig” or “Glut,” which prefers the neighbourhood of the sea to distant inland-waters, and in which the dorsal fin begins farther backwards, the distance between the commencement of the dorsal and anal fins being shorter than the head; its snout seems to be always broad. On the American side of the Atlantic other species, beside _A. anguilla_ are found in abundance: _A. bostoniensis_, _A. texana_. The largest Eels occur in lakes of the islands of the Indo-Pacific, and they play a conspicuous part in the mythology of the South-Sea Islanders and Maories; individuals of from eight to ten feet in length have been seen, and referred to several species, as _A. mauritiana_, _fidjiensis_, _obscura_, _aneitensis_, etc.

CONGER.--Scaleless. Cleft of the mouth wide, extending at least
to below the middle of the eye. Maxillary and mandibulary
teeth arranged in series, one of which contains teeth of equal
size, and so closely set as to form a cutting edge. No canine
teeth. Vomerine band of teeth short. Pectoral and vertical fins
well developed, the dorsal commencing behind the root of the
pectoral. Gill-openings large, approximate to the abdomen. The
posterior nostril opposite to the upper or middle part of the
orbit, the anterior in a tube. Eyes well developed.

The “Congers” are marine Eels; the best known species (_C. conger_) seems to be almost cosmopolitan, and is plentiful all round Europe, at St. Helena, in Japan, and Tasmania. It attains to a length of eight feet, and thrives and grows rapidly even in confinement, which is not the case with the freshwater Eel. Three other species are known, of which _C. marginatus_ from the Indian Ocean, is the most common. _Leptocephalus morrisii_ is an abnormal larval condition of the Conger.

Genera allied to _Conger_ are _Poeciloconger_, _Congromurcæna_, _Uroconger_, and _Heteroconger_.

MURÆNESOX.--Scaleless. Snout produced. Jaws with several series
of small closely set teeth, anteriorly with canines; vomer with
several long series of teeth, the middle of which is formed
by large conical or compressed teeth. Gill-openings wide,
approximate to the abdomen. Pectoral and vertical fins well
developed, the dorsal beginning above the gill-opening. Two
pairs of nostrils, the posterior opposite to the upper part or
middle of the eye.

Four species from tropical seas, _M. cinereus_ being very common in the Indian Ocean, and attaining to a length of six feet.

NETTASTOMA.--Scaleless. Snout much produced, depressed. Jaws
and vomer with bands of card-like teeth, those along the median
line of the vomer being somewhat the larger. Vertical fins well
developed; pectorals none. Gill-openings of moderate width,
open. Nostrils on the upper surface of the head, valvular; the
anterior near to the end of the snout, the posterior above the
anterior angle of the eye.

This genus lives at some depth, the Japanese species (_N. parviceps_) having been obtained at 345 fathoms. _N. melanurum_ from the Mediterranean, seems to inhabit a similar depth. _Hyoprorus_ is its Leptocephalid form.

Genera allied to _Murcænesox_ are _Saurenchelys_, _Oxyconger_, _Hoplunnis_, and _Neoconger_; in all these the nostrils have a superior or lateral position. In other genera the nostrils perforate the upper lip, as in _Myrus_, _Myrophis_, _Paramyrus_, _Chilorhinus_, _Murænichthys_, and _Ophichthys_, the last genus deserving of particular mention on account of its great range and common occurrence.

OPHICHTHYS.--Nostrils labial; extremity of the tail free, not
surrounded by a fin.

More than eighty species are known, many of which are abundant on the coasts of the tropical and sub-tropical zones. They do not attain to a large size, but many must be extremely voracious and destructive to other fishes, if we draw an inference from the formidable dentition with which their jaws and palate is armed. Other species have much more feeble, and some even obtuse teeth, better adapted for seizing Crustaceans than vigorous and slippery fishes. Some have rudimentary pectoral fins or lack them altogether. Many are highly ornamented with bands or spots, the coloration being apparently very constant in the several species.

MORINGUA.--Body scaleless, cylindrical, with the trunk much
longer than the tail. Pectorals none or small; vertical fins
but little developed, limited to the tail. Posterior nostrils
in front of the small eye. Cleft of the mouth narrow; teeth
uniserial. Heart placed far behind the branchiæ. Gill-openings
rather narrow, inferior.

Six species from freshwaters, brackish water, and the coasts of India to the Fiji Islands.

MURÆNA.--Scaleless. Teeth well developed. Gill-openings and
clefts between the branchial arches narrow. Pectoral fins none;
dorsal and anal fins well developed. Two nostrils on each side
of the upper surface of the snout; the posterior a narrow round
foramen, with or without tube; the anterior in a tube.

The Murænas are as abundantly represented in the tropical and sub-tropical zones, and have nearly the same range, as _Ophichthys_. The number of species known exceeds eighty. The majority are armed with formidable pointed teeth, well suited for seizing other fish on which they prey. Large specimens thus armed readily attack persons in and out of the water; and as some species attain a length of some six or eight feet, they are justly feared by fishermen. The minority of species have obtuse and molar-like teeth, their food consisting chiefly of Crustaceans and other hard-shelled animals. Most of the Murænas are beautifully coloured and spotted, some in a regular and constant manner, whilst in others the pattern varies in a most irregular fashion: they have quite the appearance of snakes. The Muræna of the Ancient Romans is _Muræna helena_, which is not confined to the Mediterranean, but also found in the Indian Ocean and on the coast of Australia. Its skin is of a rich brown, beautifully marked with large yellowish spots, each of which contains smaller brown spots.

_Gymnomuræna_ differs from _Muræna_ in having the fins reduced to a short rudiment near the end of the tail. Six species are known growing to a length of eight feet.

_Myroconger_ and _Enchelycore_ belong to the same sub-family as _Muræna_, but the former is provided with pectoral fins, and in the latter the posterior nostril is a long slit, and not round as in the other genera.

FIFTH ORDER--LOPHOBRANCHII.

_The gills are not laminated, but composed of small rounded lobes attached to the branchial arches. Gill-cover reduced to a large simple plate. Air-bladder simple, without pneumatic duct. A dermal skeleton composed of numerous pieces arranged in segments, replaces more or less soft integuments. Muscular system not much developed. Snout prolonged. Mouth terminal, small, toothless, formed as in Acanthopterygians._

FIRST FAMILY--SOLENOSTOMIDÆ.

_Gill-openings wide. Two dorsal fins, the rays of the anterior not articulated. All the other fins well developed._

One living genus only is known, which was preceded in the tertiary epoch by _Solenorhynchus_ (Monte Postale).

SOLENOSTOMA.--Snout produced into a long tube. Body compressed,
with very short tail. All parts covered with thin skin, below
which there is a dermal skeleton formed by large star-like
ossifications. The soft dorsal and anal fins on elevated
bases; caudal fin long. Ventral fins inserted opposite to the
anterior dorsal, close together, seven-rayed; they are free in
the male, but in the female their inner side coalesces with the
integuments of the body, a large pouch for the reception of
the eggs being formed thereby. Air-bladder and pseudobranchiæ
absent. Branchiostegals four, very thin. Intestinal tract very
simple, with a stomachic dilatation, without pyloric appendages.
Ova very small.

The dermal skeleton of this singular type is formed by star-like ossifications, four in each horizontal and vertical series on the side of the fore part of the trunk; each consists of four or three radiating branches by which it joins the neighbouring bones; on the hind part of the trunk and tail the series are diminished to two. The dorsal and abdominal profiles in front of the fins are protected by similar bones. The vertebral column is composed of eighteen abdominal and fifteen caudal vertebræ, the vertebræ gradually decreasing in length backwards, so that the shortness of the tail is caused not only by the smaller number of vertebræ, but also by their much lesser length. Neural and hæmal spines are developed. The pelvis consists of two pairs of cartilaginous laminæ, the convex margin of the anterior fitting into an angle of a dermal bone which separates the pelvis from the well-ossified humeral arch.

The singular provision for the retention and protection of the eggs has been described above (p. 162, figs. 73 and 74), and we have only to repeat here that it is the female which takes care of the progeny, and not the male as in the following family. Two or three small species are known from the Indian Ocean; they are beautifully marked, especially the male, which also appears to be of smaller size in this genus than the female.

SECOND FAMILY--SYNGNATHIDÆ.

_Gill-openings reduced to a very small opening near the upper posterior angle of the gill-cover. One soft dorsal fin; no ventrals, and, sometimes, one or more of the other fins are also absent._

Small marine fishes, which are abundant on such parts of the coasts of the tropical and temperate zones as offer by their vegetation shelter to these defenceless creatures. They are bad swimmers (the dorsal fin being the principal organ of locomotion), and frequently and resistlessly carried by currents into the open ocean or to distant coasts. All enter brackish water, some fresh water. The strata of Monte Bolca and Licata (Sicily) have, yielded evidence of their existence in the tertiary epochs; beside species of _Siphonostoma_ and _Syngnathus_ (_Pseudosyngnathus_), remains of an extinct genus, _Calamostoma_, allied to _Hippocampus_, but with a distinct caudal fin, have been found. On their propagation see p. 163, Fig. 76.

A. SYNGNATHINA.--The tail is not prehensile, and generally
provided with a caudal fin.--_Pipe-Fishes._

SIPHONOSTOMA.--Body with distinct ridges, the upper caudal
ridge continuous with the lateral line, but not with the dorsal
ridge of the trunk. Pectoral and caudal fins well developed;
dorsal fin of moderate length, opposite to the vent. Humeral
bones movable, not united into a “breast-ring.” Males with an
egg-pouch on the tail, the eggs being covered by cutaneous folds.

Two species, of which _S. typhle_ is common on the British, and generally distributed on the European coasts.

SYNGNATHUS.--Body with the ridges more or less distinct, the
dorsal ridge of the trunk not being continuous with that of the
tail. Pectoral fins well developed; caudal present. Dorsal fin
opposite or near to the vent. Humeral bones firmly united into
the breast-ring. Egg-pouch as in _Siphonostoma_.

The distribution of this genus nearly coincides with that of the family, some fifty species being known. _S. acus_, the great Pipe-fish (see Fig. 75, p. 163), is one of the most common European fishes, extending across the Atlantic and southwards to the Cape of Good Hope; it attains a length of 18 inches. Another very common species, frequently met at sea, and spread over nearly all the tropical and sub-tropical seas, is _S. pelagicus_, agreeably marked with alternate brown and silvery cross-bars.

DORYICHTHYS.--Body with the ridges well developed. Pectoral and
caudal fins present. Dorsal fin long or of moderate length,
opposite to the vent. Humeral bones firmly united. Males with
the lower ridges of the abdomen dilated, the dilated parts
forming a broad groove for the reception of the ova.

In these Pipe-fishes the ova are not received in a completely closed pouch, but glued on to the surface of the abdomen. Twenty species from tropical seas.

NEROPHIS.--Body smooth, rounded, with scarcely any of the ridges
distinct. Pectoral fin none, caudal absent or rudimentary, the
tail tapering into a point. Dorsal fin of moderate length,
opposite to the vent. The ova are attached to the soft
integument of the abdomen of the male, and are not covered by
lateral folds of the skin.

Seven species from the European seas and the Atlantic. _N. æquoreus_ (Ocean Pipe-fish), _N. ophidion_ (Straight-nosed Pipe-fish), and _N. lumbriciformis_ (Little Pipe-fish), are common on the British coasts.

PROTOCAMPUS.--The whole dermal skeleton is covered with skin.
A broad cutaneous fold runs along the back in front and behind
the dorsal; a similar fold along the abdomen. Pectoral fin none;
caudal very small.

The single species of this remarkable genus, _P. hymenolomus_, occurs in the Falkland Islands. It may be regarded as an embryonal form of _Nerophis_, the median skin-folds being evidently remains of the fringe which surrounds the body of the embryo.

The other genera belonging to this group are, _Icthyocampus_, _Nannocampus_, _Urocampus_, _Leptoichthys_, _Coelonotus_, and _Stigmatophora_.

HIPPOCAMPINA.--The tail is prehensile, and invariably without
caudal fin.--_Sea-horses._

GASTROTOKEUS.--Body depressed, the lateral line running along
the margin of the abdomen. Shields smooth. Tail shorter than the
body. Pectoral fins. No pouch is developed for the ova, which
are imbedded in the soft integument of the abdomen of the male.

_Gastrotokeus biaculeatus_, very common in the Indian Ocean to the coasts of Australia.

SOLENOGNATHUS.--Body compressed, deeper than broad. Shields
hard, rugose, with round or oval interannular plates; and
without elongate processes. Tail shorter than the body. Pectoral
fins.

Three species, from the Chinese and Australian Seas; they are the largest of Lophobranchs, _S. hardwickii_, attaining to a length of nearly two feet.

PHYLLOPTERYX.--Body compressed, or as broad as deep. Shields
smooth, but some or all of them are provided with prominent
spines or processes on the edges of the body; some of the
processes with cutaneous filaments. A pair of spines on the
upper side of the snout and above the orbit. Tail about as
long as the body. Pectoral fins. The ova are imbedded in soft
membrane on the lower side of the tail, without a pouch being
developed.

Three species from the coasts of Australia. The protective resemblances with which many Lophobranchs are furnished, attain to the highest degree of development in the fishes of this genus. Not only their colour closely assimilates that of the particular kind of seaweed which they frequent, but the appendages of their spines seem to be merely part of the fucus to which they are attached. They attain a length of 12 inches.

HIPPOCAMPUS.--Trunk compressed, more or less elevated. Shields
with more or less prominent tubercles or spines. Occiput
compressed into a crest, terminating at its supero-posterior
corner in a prominent knob (coronet). Pectoral fins. The males
carry the eggs in a sac at the base of the tail, opening near
the vent.

A singular resemblance of the head and fore part of the body to that of a horse, has given to these fishes the name of “Sea-horses.” They are abundant between and near the tropics, becoming scarcer in higher latitudes. Some twenty species are known, some of which have a wide geographical range, as they are often carried to great distances with floating objects to which they happen to be attached.--_Acentronura_ is a genus closely allied to _Hippocampus_.

SIXTH ORDER--PLECTOGNATHI.

_Teleosteous fishes with rough scales, or with ossifications of the cutis in the form of scutes or spines; skin sometimes entirely naked. Skeleton incompletely ossified, with the vertebræ in small number. Gills pectinate; a narrow gill-opening in front of the pectoral fins. Mouth narrow; the bones of the upper jaw generally firmly united. A soft dorsal fin, belonging to the caudal portion of the vertebral column, opposite to the anal; sometimes elements of a spinous dorsal besides. Ventral fin none, or reduced to spines. Air-bladder without pneumatic duct._

FIRST FAMILY--SCLERODERMI.

_Snout somewhat produced; jaws armed with distinct teeth in small number. Skin with scutes or rough. The elements of a spinous dorsal and ventral fins generally present._

Marine fishes of moderate or small size, very common in the tropical zone, but scarcer in higher latitudes. They have been found in three localities of tertiary strata, viz., at Monte Bolca, where a species of _Ostracion_ occurs, and in the Schists of Glaris, from which two genera have been described, _Acanthoderma_ and _Acanthopleurus_, closely allied to _Balistes_ and _Triacanthus_. _Glyptocephalus_ from the Isle of Sheppey has the skull of a Balistes, but its body is covered with tubercles arranged in regular series. The Scleroderms may be divided into three very natural groups:--

A. TRIACANTHINA.--The skin is covered with small, rough,
scale-like scutes. A spinous dorsal fin with from four to six
spines. A pair of strong, movable ventral spines, joined to the
pelvic bone.

To this group belong the genera _Triacanthodes_, _Hollardia_, and _Triacanthus_, represented by five species, of which _Triacanthus brevirostris_ from the Indian Ocean is the most common.

B. BALISTINA.--Body compressed, covered with movable scutes or
rough. Spinous dorsal reduced to one, two, or three spines.
Ventral fins reduced to a single pelvic prominence, or entirely
absent.

To this group belong the genera _Balistes_, _Monacanthus_, and _Anacanthus_, the last genus being distinguished by a barbel at the lower jaw.

_Balistes_, or the “File-fishes” proper, inhabit the tropical and sub-tropical seas; shoals of young are not rarely met with in mid-ocean. Some thirty species are known, many attaining a length exceeding two feet; but the majority are much smaller, and frequently beautifully and symmetrically marked. Both jaws are armed with eight strong incisor-like and obliquely truncated teeth, by which these fishes are enabled to break off pieces of corals on which they feed, or to chisel a hole into the hard shell of Mollusca, in order to extract the soft parts. They destroy an immense number of Mollusks, thus becoming most injurious to the pearl-fisheries. The first of their three dorsal spines is very strong, roughened in front like a file, and hollowed out behind to receive the second much smaller spine, which, besides, has a projection in front, at its base, fitting into a notch of the first. Thus these two spines can only be raised or depressed simultaneously, and the first cannot be forced down, unless the second has been previously depressed. The latter has been compared to a trigger, hence a second name, “Trigger-fish,” has been given to these fishes. Some species are armed with a series of short spines or tubercles on each side of the tail. Two species (_B. maculatus_ and _B. capriscus_), common in the Atlantic, sometimes wander to the British coasts.

The _Monacanthus_ are similarly distributed as the _Balistes_, and still more abundant, some fifty species being known. Their dentition is very similar, but they possess one dorsal spine only, and their rough scales are so small as to give a velvety appearance to the skin (Figs. 17 and 18, p. 48). Adult males of some of the species possess a peculiar armature on each side of the tail, which in females is much less developed or entirely absent. This armature may consist either in simple spines arranged in rows, or in the development of the minute spines of the scales into long stiff bristles, so that the patch on each side of the tail looks like a brush.

C. OSTRACIONTINA.--The integuments of the body form a hard
continuous carapace, consisting of hexagonal scutes juxtaposed
in mosaic-fashion. A spinous dorsal and ventral fins are absent;
but sometimes indicated by protuberances.

The “Coffer-fishes” (_Ostracion_) are too well known to require a lengthened description. Only the snout, the bases of the fins, and the hind part of the tail are covered with soft skin, so as to admit of free action of the muscles moving these parts. The mouth is small, the maxillary and intermaxillary bones coalescent, each jaw being armed with a single series of small slender teeth. The short dorsal fin is opposite to the equally short anal. The vertebral column consists of fourteen vertebræ only, of which the five last are extremely short, the anterior elongate. Ribs none. The carapaces of some species are three-ridged, of others four- and five-ridged, of some provided with long spines. Twenty-two species from tropical and sub-tropical seas are known.

SECOND FAMILY--GYMNODONTES.

_Body more or less shortened. The bones of the upper and lower jaw are confluent, forming a beak with a trenchant edge, without teeth, with or without median suture. A soft dorsal, caudal and anal are developed, approximate. No spinous dorsal. Pectoral fins; no ventrals._

Marine fishes of moderate or small size from tropical and sub-tropical seas. A few species live in fresh water. Fossil remains of _Diodon_ are not scarce at Monte Bolca and Licata; a distinct genus, _Enneodon_, has been described from Monte Postale. The Gymnodonts may be divided into three groups:

A. TRIODONTINA.--Tail rather long, with a separate caudal fin.
Abdomen dilatable into a very large, compressed, pendent sac,
the lower part of which is merely a flap of skin, into which the
air does not penetrate, the sac being capable of being expanded
by the very long pelvic bone. The upper jaw divided by a median
suture, the lower simple.

A single genus and species (_Triodon bursarius_) from the Indian Ocean.

B. TETRODONTINA.--Tail and caudal fin distinct. Part of the
œsophagus much distensible, and capable of being filled with
air. No pelvic bone.

“Globe-fishes” have a short, thick, cylindrical body, with well developed fins. It is covered with thick scaleless skin, in which, however, spines are imbedded of various sizes. The spines are very small, and but partially distributed over the body in some species, whilst in others they are very large, and occupy equally every part of the body. These fishes have the power of inflating their body by filling their distensible œsophagus with air, and thus assume a more or less globular form. The skin is, then, stretched to its utmost extent, and the spines protrude and form a more or less formidable defensive armour, as in a hedgehog; therefore they are frequently called “Sea-hedgehogs.” A fish thus blown out turns over and floats belly upwards, driving before the wind and waves. However, it is probable that the spines are a protection not only when the fish is on the surface and able to take in air, but also when it is under water. Some Diodonts, at any rate, are able to erect the spines about the head by means of cutaneous muscles; and, perhaps, all fill their stomach with water instead of air, for the same purpose and with the same effect. In some Diodonts the spines are fixed, erect, not movable. The Gymnodonts generally, when taken, produce a sound, doubtless by the expulsion of air from the œsophagus. Their vertebral column consists of a small number of vertebræ, from 20 to 29, and their spinal chord is extremely short. All these fishes have a bad reputation, and they are never eaten; indeed, some of them are highly poisonous, and have caused long continued illness and death. Singularly, the poisonous properties of these fishes vary much as regards intensity, only certain individuals of a species, or individuals from a certain locality, or caught at a certain time of the year, being dangerous. Therefore it is probable that they acquire their poisonous quality from their food, which consists in corals and hard-shelled Mollusks and Crustaceans. Their sharp beaks, with broad masticating posterior surface, are admirably adapted for breaking off branchlets of coral-stocks, and for crushing hard substances.

TETRODON (including _Xenopterus_).--Both the upper and lower
jaws are divided into two by a mesial suture.

Extremely numerous in tropical and sub-tropical zones, more than sixty species being known. In some of the species the dermal spines are extremely small, and may be absent altogether. Many are highly ornamented with spots or bands. A few species live in large rivers--thus _T. psittacus_ from Brazil; _T. fahaka_, a fish well known to travellers on the Nile, and likewise abundant in West African rivers; _T. fluvi__atilis_ from brackish water and rivers of the East Indies. The species figured is one of the smallest, about six inches long, and common in the Indo-Pacific.

DIODON.--Jaws without mesial suture, so that there is only one
undivided dental plate above and one below.

In these fishes, as well as in some closely allied genera, the dermal spines are much more developed than in the Tetrodonts; in some the spines are erectile, as in _Diodon_, _Atopomycterus_, _Trichodiodon_, and _Trichocyclus_; in others they are stiff and immovable, as in _Chilomycterus_ and _Dicotylichthys_. Seventeen species are known, of which _Diodon hystrix_ is the most common as it is the largest, growing to a length of two feet. It is spread over the Tropical Atlantic as well as Indo-Pacific, as is also a smaller, but almost equally common species, _Diodon maculatus_.

C. MOLINA.--Body compressed, very short; tail extremely short,
truncate. Vertical fins confluent. No pelvic bone.

The “Sun-fishes” (_Orthagoriscus_) are pelagic fishes, found in every part of the oceans within the tropical and temperate zones. The singular shape of their body and the remarkable changes which they undergo with age, have been noticed above (p. 175, Figs. 93, 94). Their jaws are undivided in the middle, comparatively feeble, but well adapted for masticating their food, which consists of small pelagic Crustaceans. Two species are known. The common Sun-fish, _O. mola_, which attains to a very large size, measuring seven or eight feet, and weighing as many hundredweights. It has a rough, minutely granulated skin. It frequently approaches the southern coasts of England and the coasts of Ireland, and is seen basking in calm weather on the surface. The second species, _O. truncatus_, is distinguished by its smooth, tessellated skin, and one of the scarcest fishes in collections. The shortness of the vertebral column of the Sun-fishes, in which the number of caudal vertebra is reduced to seven, the total number being seventeen, and the still more reduced length of the spinal chord have been noticed above (p. 96).

THIRD SUB-CLASS--CYCLOSTOMATA.

_Skeleton cartilaginous and notochordal, without ribs and without real jaws. Skull not separate from the vertebral column. No limbs. Gills in the form of fixed sacs, without branchial arches, six or seven in number on each side. One nasal aperture only. Heart without bulbus arteriosus. Mouth anterior, surrounded by a circular or subcircular lip, suctorial. Alimentary canal straight, simple, without coecal appendages, pancreas or spleen. Generative outlet peritoneal. Vertical fins rayed._

The Cyclostomes are most probably a very ancient type. Unfortunately the organs of these creatures are too soft to be preserved, with the exception of the horny denticles with which the mouth of some of them is armed. And, indeed, dental plates, which are very similar to those of _Myxine_, are not uncommon in certain strata of Devonian and Silurian age (see p. 193). The fishes belonging to this sub-class may be divided into two families--

FIRST FAMILY--PETROMYZONTIDÆ.

_Body eel-shaped, naked. Subject to a metamorphosis; in the perfect stage with a suctorial mouth armed with teeth, simple or multicuspid, horny, sitting on a soft papilla. Maxillary, mandibulary, lingual, and suctorial teeth may be distinguished. Eyes present (in mature animals). External nasal aperture in the middle of the upper side of the head. The nasal duct terminates without perforating the palate. Seven branchial sacs and apertures on each side behind the head; the inner branchial ducts terminate in a separate common tube. Intestine with a spiral valve. Eggs small. The larvæ without teeth, and with a single continuous vertical fin._

“Lampreys” are found in the rivers and on the coasts of the temperate regions of the northern and southern hemispheres. Their habits are but incompletely known, but so much is certain that at least some of them ascend rivers periodically, for the purpose of spawning, and that the young pass several years in rivers, whilst they undergo a metamorphosis (see p. 170). They feed on other fishes, to which they suck themselves fast, scraping off the flesh with their teeth. Whilst thus engaged they are carried about by their victim; Salmon have been captured in the middle course of the Rhine with the Marine Lamprey attached to them.

PETROMYZON.--Dorsal fins two, the posterior continuous with the
caudal. The maxillary dentition consists of two teeth placed
close together, or of a transverse bicuspid ridge; lingual teeth
serrated.

The Lampreys belonging to this genus are found in the northern hemisphere only; the British species are the Sea-Lamprey (_P. marinus_), exceeding a length of three feet, and not uncommon on the European and North American coasts; the River-Lamprey or Lampern (_P. fluviatilis_), ascending in large numbers the rivers of Europe, North America, and Japan, and scarcely attaining a length of two feet; the “Pride” or “Sand-Piper” or Small Lampern (_P. branchialis_), scarcely twelve inches long, the larva of which has been long known under the name of _Ammocoetes_.

_Ichthyomyzon_ from the western coasts of North America is said to have a tricuspid maxillary tooth.

MORDACIA.--Dorsal fins two, the posterior continuous with the
caudal. The maxillary dentition consists of two triangular
groups, each with three conical acute cusps; two pairs of
serrated lingual teeth.

A Lamprey _(M. mordax_) from the coasts of Chile and Tasmania. This fish seems to be provided sometimes with a gular sac, like the following.[47]

GEOTRIA.--Dorsal fins two, the posterior separate from the
caudal. Maxillary lamina with four sharp flat lobes; a pair of
long pointed lingual teeth.

Two species, one from Chile and one from South Australia. They grow to a length of two feet, and in some specimens the skin of the throat is much expanded, forming a large pouch. Its physiological function is not known. The cavity is in the subcutaneous cellular tissue, and does not communicate with the buccal or branchial cavities. Probably it is developed with age, and absent in young individuals. In all the localities in which these Extra-european Lampreys are found, _Ammocoetes_ forms occur, so that there is little doubt that they undergo a similar metamorphosis as _P. branchialis_.

SECOND FAMILY--MYXINIDÆ.

_Body eel-shaped, naked. The single nasal aperture is above the mouth, quite at the extremity of the head, which is provided with four pairs of barbels. Mouth without lips. Nasal duct without cartilaginous rings, penetrating the palate. One median tooth on the palate, and two comb-like series of teeth on the tongue_ (see Fig. 101). _Branchial apertures at a great distance from the head; the inner branchial ducts lead into the œsophagus. A series of mucous sacs along each side of the abdomen. Intestine without spiral valve. Eggs large, with a horny case provided with threads for adhesion._

The fishes of this family are known by the names of “Hag-Fish,” “Glutinous Hag,” or “Borer;” they are marine fishes with a similar distribution as the Gadidæ, being most plentiful in the higher latitudes of the temperate zones of the northern and southern hemispheres. They are frequently found buried in the abdominal cavity of other fishes, especially Gadoids, into which they penetrate to feed on their flesh. They secrete a thick glutinous slime in incredible quantities, and are therefore considered by fishermen a great nuisance, seriously damaging the fisheries and interfering with the fishing in localities where they abound. _Myxine_ descends to a depth of 345 fathoms, and is generally met with in the Norwegian Fjords at 70 fathoms, sometimes in great abundance.

MYXINE.--One external branchial aperture only on each side of
the abdomen, leading by six ducts to six branchial sacs.

Three species from the North Atlantic, Japan, and Magelhæn’s Straits.

BDELLOSTOMA.--Six or more external branchial apertures on each
side, each leading by a separate duct to a branchial sac.

Two species from the South Pacific.

FOURTH SUB-CLASS--LEPTOCARDII.

_Skeleton membrano-cartilaginous and notochordal, ribless. No brain. Pulsating sinuses in place of a heart. Blood colourless. Respiratory cavity confluent with the abdominal cavity; branchial clefts in great number, the water being expelled by an opening in front of the vent. Jaws none._

This sub-class is represented by a single family (_Cirrostomi_) and by a single genus (_Branchiostoma_);[48] it is the lowest in the scale of fishes, and lacks so many characteristics, not only of this class, but of the vertebrata generally, that Hæckel, with good reason, separates it into a separate class, that of _Acrania_. The various parts of its organisation have been duly noticed in the first part of this work.

The “Lancelet” (_Branchiostoma lanceolatum_, see Fig. 28, p. 63), seems to be almost cosmopolitan within the temperate and tropical zones. Its small size, its transparency, and the rapidity with which it is able to bury itself in the sand, are the causes why it escapes so readily observation, even at localities where it is known to be common. Shallow, sandy parts of the coasts seem to be the places on which it may be looked for. It has been found on many localities of the British, and generally European coasts, in North America, the West Indies, Brazil, Peru, Tasmania, Australia, and Borneo. It rarely exceeds a length of three inches. A smaller species, in which the dorsal fringe is distinctly higher and rayed, and in which the caudal fringe is absent, has been described under the name of _Epigionichthys pulchellus_; it was found in Moreton Bay.