Fig. 115.—Dentition of Notidanus indicus. a, teeth in function; b, teeth in reserve; u, upper, and l, lower, tooth, of natural size.
Fourth Family—Notidanidæ.
No nictitating membrane. One dorsal fin only, without spine, opposite to the anal.
Notidanus.—Dentition unequal in the jaws: in the upper jaw one or two pairs of awl-shaped teeth, the following six being broader, and provided with several cusps, one of which is much the strongest. Lower jaw with six large comb-like teeth on each side, beside the smaller posterior teeth. Spiracles small, on the side of the neck. No pit at the root of the caudal fin. Gill-openings wide, six in number in Hexanchus, seven in Heptanchus.
Four species are known, distributed over nearly all the tropical and sub-tropical seas; they attain to a length of about fifteen feet. Fossil teeth belonging to this type have been found in Jurassic and later formations (Notidanus and Aellopos).
Fifth Family—Scylliidæ.
Two dorsal fins, without spine: the first above or behind the ventrals; anal fin present. No nictitating membrane. Spiracle always distinct. Mouth inferior. Teeth small, several series generally being in function.
Scyllium.—The origin of the anal fin is always in advance of that of the second dorsal. Nasal cavity separate from the mouth. Teeth small, with a middle longer cusp, and generally one or two small lateral cusps arranged in numerous series. Eggs similar to those of the Rays (Fig. [79], p. 167).
The fishes of this genus are of small size, and commonly called “Dog-fishes.” They are coast fishes, living on the bottom, and feeding on Crustaceans, dead fishes, etc. None of the eight species known have a very wide distribution, but where they occur they are generally sufficiently abundant to prove troublesome to fishermen. They inhabit most parts of the temperate and tropical seas. On the British coasts two species are found, the “Larger” and “Lesser spotted Dog-fish,” Scyllium canicula and Scyllium catulus, which are said to be more plentiful among the Orkney Islands than elsewhere. They are scarcely ever brought to market; but the fishermen of some localities do not disdain to eat them. Their flesh is remarkably white, a little fibrous, and dry. In the Orkneys they are skinned, split up, cleaned, and then spread out on the rocks to dry for home consumption. The skins are used for smoothing down cabinet-work. It would be worth while to apply the fins of these and other Sharks, which are so extensively used in China for making gelatine soups, to the same purpose in this country, or to dry them for exportation to the East. Most of the species of Dog-fishes are spotted, and those of the allied genera, Parascyllium and Chiloscyllium, very handsomely ornamented.