. Fishes. Fishes. 200 The True Sharks triangular serrate teeth, very massive in substance, and without denticles. As only the teeth are known, the actual relations of the several species of Corax are not certainly known, and they may belong to the Lam- nid(E. Family Sphymidae, or Ham- mer-head Sharks.—The Sphyrni- dcB, or hammer-headed sharks, are exactly like the Carcha- riidcE except that the sides of the head are produced, so as to give it the shape of a ham- Fig. 143.—Teeth of Corax mer or of a kidney, the eye ^"*" °"' "^' being on the produced outer edge. The species a
. Fishes. Fishes. 200 The True Sharks triangular serrate teeth, very massive in substance, and without denticles. As only the teeth are known, the actual relations of the several species of Corax are not certainly known, and they may belong to the Lam- nid(E. Family Sphymidae, or Ham- mer-head Sharks.—The Sphyrni- dcB, or hammer-headed sharks, are exactly like the Carcha- riidcE except that the sides of the head are produced, so as to give it the shape of a ham- Fig. 143.—Teeth of Corax mer or of a kidney, the eye ^"*" °"' "^' being on the produced outer edge. The species are few, but mostly widely distributed; rather large, voracious sharks with small sharp teeth. The true hammer-head, Sphyrna zygccna, Fig. 143, is common from the Mediterranean to Cape Cod, California, Hawaii, and Japan. The singular form of its head is one of the most ex- traordinary modifications shown among fishes. The bonnet-head {Sphyrna tiburo) has the head kidney-shaped or crescent-shaped. It is a smaller fish, but much the same in distribution and habits. Intermediate forms occur, so that with all the actual differences we must place the SpJiyrnidce all in one genus. Fossil hammer- heads occur in the Miocene, but their teeth are scarcely different from those of Carcharias. Sphyrna prisca, described by Agassiz, is the primeval species. The Order of Tectospondyli.—The sharks and rays having no anal fin and with the calcareous lamellae arranged in one or more rings around a central axis constitute a natural group to which, following Woodward, we may apply the name of Tecto- spondyli. The Cyclospondyli (Sqiialidce, etc.) with one ring only of calcareous lamellae may be included in this order, as also the rays, which have tectospondylous vertebras and dift'er from the sharks as a group only in having the gill-openings relegated to the lower side by the expansion of the pectoral fins. The group of rays and Basse's order of Cyclospondyli we may consider each as a suborde
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