Fig. 134.—Dicerobatis draco, from Misol.
The species of these two last genera are not yet well distinguished; about five of Dicerobatis and two of Ceratoptera are known from tropical and temperate seas, but their occurrence in the latter is rather sporadic. Some of them, if not all, attain an enormous size. One mentioned by Risso, taken off Messina, weighed 1250 pounds. Several observers speak of having seen them in pairs, the male being usually the smaller. Of a pair mentioned by Risso the female was first taken, and the male remained hovering about the boat for three days, and was afterwards found floating dead on the surface. Still larger individuals, but of uncertain species, are mentioned by Lacépède, who says that one taken at Barbadoes required seven yoke of oxen to draw it. A sketch of another, which was said to be twenty feet long, was sent to Lacépède; and Sonnini speaks of one which appeared to him to be longer and wider than the ship in which he was sailing. A fœtus taken from the uterus of the mother captured at Jamaica, and preserved in the British Museum, is five feet broad, and weighed twenty pounds. The mother measured fifteen feet in width as well as in length, and was between three and four feet thick. The capture of “Devil-fishes” of such large size is attended with danger, as they not rarely attack and capsize the boat. They are said to be especially dangerous when they accompany their young, of which they bring forth one only at a time.
SECOND SUB-ORDER—HOLOCEPHALA.
One external gill-opening only, covered by a fold of the skin, which encloses a rudimentary cartilaginous gill-cover; four branchial clefts within the gill-cavity. The maxillary and palatal apparatus coalescent with the skull.
This suborder is represented in the living fauna by one family only, Chimæridæ; it forms a passage to the following order of fishes, the Ganoids. In external appearance, and with regard to the structure of their organs of propagation, the Chimæras are Sharks (See Fig. [96], p. 184). The males are provided with “claspers” in connection with the ventral fins, and the ova are large, encased in a horny capsule, and few in number; and there is no doubt that they are impregnated within the oviduct, as in Sharks. Chimæras are naked, but, as in Scylliidæ, very young individuals possess a series of small “placoid” spines, which occupy the median line of the back, and remind us of similar dermal productions in the Rays. The males, besides, are provided with a singular erectile appendage, spiny at its extremity, and received in a groove on the top of the head. On the other hand, the relations of the Chimæras to the Ganoid, and, more especially, Dipnoous type become manifest in their notochordal skeleton and continuity of cranial cartilage. The spine in front of the first dorsal fin is articulated to the neural apophysis, and not merely implanted in the soft parts, and immovable as in Sharks. A cartilaginous operculum makes its appearance, and the external gill-opening is single. The dentition is that of a Dipnoid, each “jaw” being armed with a pair of broad dental plates, with the addition of a pair of smaller cutting teeth in the upper “jaw.” Fossils of similar dental combination are not rare in strata, commencing from the Lias and the bottom of the Oolitic series; but it is impossible to decide in every case whether the fossil should be referred to the Holocephalous or Dipnoous type. According to Newberry, Chimæroid fishes commence in the Devonian with Rhynchodus, the remains of which were discovered by him in Devonian rocks of Ohio. Undoubted Chimæroids are Elasmodus, Psaliodus, Ganodus, Ischyodus, Edaphodon, and Elasmognathus, principally from mesozoic and tertiary formations. Very similar fossils occur in the corresponding strata of North America. A single species of Callorhynchus has been discovered by H. Hector in the Lower Greensand of New Zealand.
The living Chimæras are few in number, and remain within very moderate dimensions, probably not exceeding a length of five feet, inclusive of their long filamentous, diphycercal tail. They are referred to two genera.
Chimæra.—Snout soft, prominent, without appendage. The dorsal fins occupying the greater part of the back, anterior with a very strong and long spine. Longitudinal axis of the tail nearly the same as that of the trunk, its extremity being provided with a low fin above and below, similar in form to a dorsal and anal fin. Anal fin very low.
Three species are known: Ch. monstrosa, from the coasts of Europe and Japan and the Cape of Good Hope; Ch. colliei from the west coast of North America; and Ch. affinis from the coast of Portugal. (See Fig. [96], p. 184.)
Callorhynchus.—Snout with a cartilaginous prominence, terminating in a cutaneous flap. Two dorsal fins, the anterior with a very strong and long spine. Extremity of the tail distinctly turned upwards, with a fin along its lower edge, but without one above. Anal fin close to the caudal, short and deep.