. The Cambridge natural history. Zoology. 448 FISHES CHAP. its lateral sensory canals in a series of incomplete calcified rings, as in the Holocephali. Fam. 8. Carchariidae. — gharks with two dorsal fins, the first in front of the pelvic fins and the second opposite the anal fin, both devoid of spines. Tail without lateral keels. Preoraf rostrum elongated. Mouth crescentic. Eyes with nictitating membranes. Spiracles small or absent. Vertebrae asterospondylic. Teeth usually consisting of a single triangular cusp, with smooth, trenchant, or serrated margins, rarely with basal cusps; generally wi
. The Cambridge natural history. Zoology. 448 FISHES CHAP. its lateral sensory canals in a series of incomplete calcified rings, as in the Holocephali. Fam. 8. Carchariidae. — gharks with two dorsal fins, the first in front of the pelvic fins and the second opposite the anal fin, both devoid of spines. Tail without lateral keels. Preoraf rostrum elongated. Mouth crescentic. Eyes with nictitating membranes. Spiracles small or absent. Vertebrae asterospondylic. Teeth usually consisting of a single triangular cusp, with smooth, trenchant, or serrated margins, rarely with basal cusps; generally with an axial cavity when fully developed. Viviparous. The family comprises about twenty genera, and approximately sixty species; found in all seas, often in mid-ocean. Amongst the more important genera may be mentioned Carcharias [Carcliarliinus), Galeocerdo, Triahis, Thcdassorlnnus, Galeus, Jllus- telus and Fig. 255.—The Blue Shark {Carcharias glaucus). (From Miiller and Henle.) Species of Carcharias are found in nearly all tropical and sub- tropical seas. The genus is a somewhat comprehensive one, and groups of its species have been distinguished as sub-genera under the names of Prionodon, Hypoprion, ScoHodon, Ajmonodoni'- etc. One of the most widely distributed of the thirty to forty species is the Blue Shark, C. {Prionodon) glaucus (Fig. 255), of the Atlantic and Pacific Oceans, which may grow to a length of 25 feet, although the young forms not infrequently captured in British waters do not exceed 6 to 8 feet. It is a slender, swift, pelagic Shark, of a slaty-blue colour above and white underneath, and a voracious hunter of other Pishes. C. nicaraguensis, a Shark about 7 feet long, is confined to Lake Nicaragua and its outlet the Eio San Juan, and is one of the very rare strictly freshwater Sharks. Galeocerdo is a large Shark found in temperate and tropical waters, but one species, G. arcticiis, is confined to Arctic seas. The variegated G. tigrinus, or
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
