Fig. 333.—Basking Shark, Cetorhinus maximus (Gunner). France.
Family Rhineodontidæ.—The whale-sharks, Rhineodontidæ, are likewise sluggish monsters with feeble teeth and keeled tails. From Cetorhinus they differ mainly in having the last gill-opening above the pectorals. There is probably but one species, Rhineodon typicus, of the tropical Pacific, straying northward to Florida, Lower California, and Japan.
The Carcharioid Sharks, or Requins.—The largest family of recent sharks is that of Carchariidæ (often called Galeorhinidæ, or Galeidæ), a modern offshoot from the Lamnoid type, and especially characterized by the presence of a third eyelid, the nictitating membrane, which can be drawn across the eye from below. The heterocercal tail has no keel; the end is bent upward; both dorsal fins are present, and the first is well in front of the ventral fins; the last gill-opening over the base of the pectoral, the head normally formed; these sharks are ovoviviparous, the young being hatched in a sort of uterus, with or without placental attachment.
Some of these sharks are small, blunt-toothed, and innocuous. Others reach a very large size and are surpassed in voracity only by the various Lamnidæ.
The genera Cynias and Mustelus, comprising the soft-mouthed or hound-sharks, have the teeth flat and paved, while well-developed spiracles are present. These small, harmless sharks abound on almost all coasts in warm regions, and are largely used as food by those who do not object to the harsh odor of shark's flesh. The best-known species is Cynias canis of the Atlantic. By a regular gradation of intermediate forms, through such genera as Rhinotriacis and Triakis with tricuspid teeth, we reach the large sharp-toothed members of this family. Galeus (or Galeorhinus) includes large sharks having spiracles, no pit at the root of the tail, and with large, coarsely serrated teeth. One species, the soup-fin shark (Galeus zyopterus), is found on the coast of California, where its fins are highly valued by the Chinese, selling at from one to two dollars for each set. The delicate fin-rays are the part used, these dissolving into a finely flavored gelatine. The liver of this and other species is used in making a coarse oil, like that taken from the dogfish. Other species of Galeus are found in other regions, Galeus galeus being known in England as tope, Galeus japonicus abounding in Japan.
Fig. 334.—Soup-fin Shark, Galeus zyopterus (Jordan & Gilbert). Monterey.
Galeocerdo differs mainly in having a pit at the root of the tail. Its species, large, voracious, and tiger-spotted, are found in warm seas and known as tiger-sharks (Galeocerdo maculatus in the Atlantic, Galeocerdo tigrinus in the Pacific).
The species of Carcharias (Carcharhinus of Blainville) lack the spiracles. These species are very numerous, voracious, armed with sharp teeth, broad or narrow, and finely serrated on both edges. Some of these sharks reach a length of thirty feet. They are very destructive to other fishes, and often to fishery apparatus as well. They are sometimes sought as food, more often for the oil in their livers, but, as a rule, they are rarely caught except as a measure for getting rid of them. Of the many species the best known is the broad-headed Carcharias lamia, or cub-shark, of the Atlantic. This the writer has taken with a great hook and chain from the wharves at Key West. These great sharks swim about harbors in the tropics, acting as scavengers and occasionally seizing arm or leg of those who venture within their reach. One species (Carcharias nicaraguensis) is found in Lake Nicaragua, the only fresh-water shark known, although some run up the brackish mouth of the Ganges and into Lake Pontchartrain. Carcharias japonicus abounds in Japan.