132 PALEONTOLOGY. 



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 Gaieocerdo. The species 

 are found in both the cretaceous and tertiary for- 

 mations ; Gaieocerdo aduncus (fig. 48) is from the 

 miocene of Europe and America. In the same 

 tertiary series are found the teeth of the Hemipris- 

 tis serra, Ag. (fig. 49). 



Odontaspis (Ag.), presents a form of tooth most 

 Fig. 49. like that in the blue sharks (Lamna) of the present 



Hemipristis n . o r\ 7 , • . n 



serra. seas - Species oi Odontaspis occur m the cretaceous 

 (Miocene.) an( i tertiary beds. The 0. Hopei (fig. 50) 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 Hunterian 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 Carcha- 

 Fig. 50. r ^ as > 2 inches 3 lines at its " longest side," from a 

 Odontaspis shark which measured 20 feet in length. If the 

 fr , \ tooth of the fossil Carcharodon bore the same pro- 



(Liocene.) *- 



portion to the body of the fish, this must have 

 been about sixty feet in length* Teeth of Carcharodon have 

 been obtained from the Eed Crag of Suffolk, measuring 

 upwards of six inches in length. The microscopic structure of 

 the teeth in sharks is illustrated by the longitudinal section of 



* See the Author's Catalogue of Fossil Reptilia and Pisces, in Mus. E. 

 Coll. of Surgeons. Lond. 4to, 1854, p. 124, No. 431. 



