30 SHARKS. 



triangular plates with a broad base, sharp apex, and trenchant or 

 finely dentated edges. The anterior surface is nearly flat, the poste- 

 rior shghtly convex : the teeth of the lower jaw are rather narrower, 

 and thicker, and somewhat smaller than those of the upper jaw. 

 The dentition figured(l) is that of the great and formidable *' white 

 shark" of navigators, — the type of the subgenus Carcharodon of 

 Miiller. In the United Service Museum there are preserved the 

 jaws of a Carcharodon, of which the upper one measures four feet and 

 the lower one three feet eight inches, following the curvature. The 

 length of the largest tooth is two inches, the breadth of its base one 

 inch nine lines : the total length of the shark was thirty-seven feet. 



Fossil teeth precisely corresponding in form with those of the Car- 

 charodon occur abundantly in the tertiary formations of both the old and 

 new continents ; some of these teeth exhibit the extraordinary dimen- 

 sions of six inches in length, and five inches across the base. If, there- 

 fore, the proportions of these extinct Carcharodons corresponded with 

 those of the existing species, they must have equalled the great 

 mammiferous whales in size ; and, combining with the organization of 

 the shark its bold and insatiable character, they must have consti- 

 tuted the most terrific and irresistible of the predaceous monsters of 

 the ancient deep. 



In the hlue-shark, f Car charias glaucus, Cuv.), the teeth of the 

 lower jaw are longer and narrower than in the white-shark, and ap- 

 proach nearer to the form characteristic of the genus Lamna ; they 

 may be distinguished, however, by their broader base, the angles of 

 which are less produced downwards, and by their finely dentated edges. 



In the subgenus Physodon, which is nearly allied to Carcharias, the 

 teeth of one or two median rows are disproportionately small. 



The teeth of the hammer-headed sharks fZygcsnaJ, are triangular 

 flattened plates, with finely dentated margins, as in Carcharias, but 

 the points are bent backwards, and the posterior margin is concave. (2) 



In the genus Galeus, to which the grey-shark or tope of our coast 

 belongs, the teeth are relatively thicker than in the Zygcena, and the 

 posterior margin is notched, with the basal part produced backward, 

 and divided into three or more denticles : the anterior margin is 



(1)P1. 4, fig. 1. (2)P1. 4, fig. 2. 



