Fig. 124.—Læmargus borealis, Greenland Shark.
Echinorhinus.—Two very small dorsal fins, without spine, the first opposite to the ventrals. Skin with scattered large round tubercles. Nostrils midway between the mouth and the end of the snout. Teeth equal in both jaws, very oblique, the point being turned outwards; several strong denticulations on each side of the principal point. Spiracles small.
The “Spinous Shark” is readily recognised by the short bulky form of its body, short tail, and large spinous tubercles. It is evidently a ground-shark, which probably lives at some depth and but accidentally comes to the surface. More frequently met with in the Mediterranean, it has been found several times on the south coast of England, and near the Cape of Good Hope.
Euprotomicrus and Isistius are two other genera of this family; they are pelagic and but little known.
Ninth Family—Rhinidæ.
No anal fin; two dorsal fins. Spiracles present. Pectoral fins large, with the basal portion prolonged forwards, but not grown to the head.
Rhina.—Head and body depressed, flat; mouth anterior. Gill-openings rather wide, lateral, partly covered by the base of the pectoral. Spiracles wide, behind the eyes. Teeth conical, pointed, distant. Dorsal fins on the tail.
The “Angel-fish,” or “Monk-fish” (Rh. squatina), approaches the Rays as regards general form and habits. Within the temperate and tropical zones it is almost cosmopolitan, being well known on the coasts of Europe, eastern North America, California, Japan, South Australia, etc.; it does not seem to exceed a length of five feet; it is viviparous, producing about twenty young at a birth.
Extinct forms, closely allied to the “Angel-fish,” are found in the Oolite, and have been described as Thaumas. The carboniferous genus, Orthacanthus, may have been allied to this family, but it was armed with a spine immediately behind the head.