. Natural history. Zoology. 518 PISCES—SUB-CLASS IV.—ELASMpBRANCHIT. The dog-Bshes and allied members of this family differ from the foregoing sharks with the mouth terminal by the backward position of the second dorsal fin which occupies a position immediately over, or Family Scyl- behind the line of the pelvic pair. The teeth, of which liidm. several series are generally in use, are of small size, the eye lacks the nictitating membrane, and spiracles are present on the head. The dog-tishes, of which there are two species from Britisli waters, form the genus ScylUum; most of the species havin
. Natural history. Zoology. 518 PISCES—SUB-CLASS IV.—ELASMpBRANCHIT. The dog-Bshes and allied members of this family differ from the foregoing sharks with the mouth terminal by the backward position of the second dorsal fin which occupies a position immediately over, or Family Scyl- behind the line of the pelvic pair. The teeth, of which liidm. several series are generally in use, are of small size, the eye lacks the nictitating membrane, and spiracles are present on the head. The dog-tishes, of which there are two species from Britisli waters, form the genus ScylUum; most of the species having their skins elegantly spotted. Much larger is the Indian zebra-shark (Stegostoma), growing to some fifteen feet in length, and taking its name from its zebra or tiger-like coloration. Mention must also be made of the sharks of the genus Grossorhinns, from Japan and Australia, not only on account of the circum- stance that they are deep-water forms, but likewise from the presence of leaf-like outgrowths of the skin of the sides of the head ; such appendages beiug probably for the purpose of attracting prey within reach of the jaws. The Port Jackson shark, together with three allied species, form the genus Cestracion (or more properly, Cestracium ^), which now alone constitutes a family easily recognised by the peculiar character of tlie Family dentition, and likewise by the presence of a spine in the Ceslraciid'V. front portion of each dorsal fin. Whereas in the forepart of both jaws the numerous rows of teeth are sharp and cusped, on the sides and hinder region they form a pavement-like structure, arranged in oblique rows ; the teeth in some of these rows being much larger than in the others. The mouth is situated at the extremity of the muzzle, and the eye is unprovided with a nicti tating membrane. These sharks, which do not grow to more than about five feet in length, are widely dis- tributedin thewarmer seas. Although we Fig. 37.—Port Jackson Shaek. are still very i
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