SQUALIDE.
(Sharks.) The well-marked, saw-shaped tooth (fig. 32), so closely re sembles the lower jaw-teeth of the sharks, called " grisets " by the French (Notidanus, Cuv.), as to be referred to that genus by Agassiz. Such teeth nevertheless occur in strata of oolitic age (Notidanus Miinsteri, Ag., fig. 32). Other species--e. g., N. pectinatus—are found in the chalk of Kent ; and N. serra tissimus, in the eocene clay at Sheppy.
The tooth (fig. 33) on which Agassiz has founded the genus Corax, indicates by its close resemblance to those of Carcharias, its relationship with the true sharks (Squalid). Most of the species of Corax, including C. falcatus, are cretaceous ; a few are tertiary : all are extinct.
Another form of shark's tooth, deeply notched at one mar gin, and with the rest of the border finely denticulate, resembles more that of the "topes" or gray sharks (Galeus, Cuv.), and is referred by Agassiz to the genus Galeocerdo. The species are found in both the cretaceous and tertiary forma tions ; Galeocerdo aduncue (fig. 34) is from the miocene of Europe and America. In the same tertiary series are found the teeth of the Hemi pristis serra, Ag. (fig. 35).
Odontaspis (Ag.), presents a form of tooth most like that in the blue sharks (Lamna) of the pre sent seas. Species of Odontaspis occur in the cre taceous and tertiary beds. The 0. Hopei (fig. 36) is from the London clay of Sheppy. It indicates a very destructive and formidable species of shark.
Teeth shaped like those of the white sharks (Carcharias), but solid and usually of large size, are referred to the genus Carcharodon. One of these teeth, from miocene beds, Malta, in the Hun terian Museum, London, measures 5 inches 10 lines at its longest side, and 4 inches 8 lines across the base. By the side of it is placed a tooth of an existing Carcharias, 2 inches 3 lines at its " longest side," from a shark which measured 20 feet in length. If the tooth of the fossil Carcharodon bore the same proportion to the body of the fish, this must have been about sixty feet in Teeth of Carcharoclon have been obtained from the Red Crag of Suffolk, mea suring upwards of six inches in length. The microscopic structure of the teeth in sharks is illustrated by the longitudinal section of a fossil from Sheppy, showing the outer hard layer of "vitrodentine," and the "vaso-dentine" forming the body of the tooth. With these fossil teeth of sharks are found, though sparingly, in both the cretaceous and tertiary beds, petrified bodies of vertebras, showing by their extreme shortness in com parison with their breadth, by their biconcavity, and the fissures on the external surface (as shown on the lower figure of cut 37), that they belonged to a shark closely allied to the Porbeagle (Lamm, Cuv.)