366 Davis — On the Fossil Fish of the Cretaceous Formations of Scandinavia. 



founded on teeth and vertebrae which resemble those of Selache (Cetorhinus) 

 maxima, occurs in the Tertiary strata of Antwerp, Italy, and Germany. The 

 genus Carcharodon was established by Miiller and Henle, who separated the 

 species of this genus from those of Carcharias.* The type of the new genus was 

 Carcharodon rondeletii, Miill. and Henle. The latter authors still further distinguished 

 the two genera by the microscopical examination of their teeth. Tliose of the 

 genus Carcharias were found to be hollow, whilst those of Carcharodon were solid, 

 like those of the genera constituting the Lamnidse. The Carcharodon was 

 therefore removed, and incorporated with the family of Lamnidse. The type of 

 the genus is the single existing species C. rondeletii. The teeth of this species 

 attain a length of an inch and a-half, and the entire length of the fish approaches 

 forty feet. The teeth of the Tertiary representative of the genus C. megalodon are 

 four or five inches in length ; and if the fish was proportionally large it must have 

 been of extraordinary size. The teeth of C. rondeletii exhibit considerable variety 

 of form, but are all triangular, with serrated margins, but without lateral cones or 

 denticles. The teeth in front on each side the symphysis of the jaws are higher 

 in the crown and narrower at the base than those located further back ; the posterior 

 teeth gradually diminish in size, and, at the same time, become very broad 

 in comparison to the height. The teeth of the lower jaw are more lance-like than 

 those of the upper one, which are more uniformly triangular, with straighter 

 margins. 



The second dorsal fin and the anal are small. The lower lobe of the caudal 

 fin is well developed, with a keel along the side, and there is a pit at its root. 



Agassiz, in addition to the species of Carcharodon found fossil, which closely 

 resembled the existing one, included in the genus a number of others which 

 were unlike the type in possessing well-developed lateral denticles on their 

 anterior and posterior borders. Whilst recognising the irregularity in form, f it did 

 not appear of sufficient impoi'tance to justify the establishment of a new genus. 

 Other species, in addition to the lateral denticles, depart still further from the 

 type, in having the anterior border very much arched. Such species are 

 Carcharodon leptodon, C. disauris, C. tnecfalotis, C. heterodon, C. aiiriciilatiis,% 

 C toliapicus,^ and others. Agassiz is more specific in the statement of his 

 opinion with respect to these species, that they ought, at some time, to be 

 isolated with others to form a genus apart. He is confirmed in this opinion by 

 the fact that in the living species the tendency of the teeth to assume an arched 

 form is scarcely perceptible, whilst it is constantly seen in some other genera of 

 Lamnidse, and in true examples of Carcharias. 



*Syst. beschrieb. Plagiostom, p. 70. 1841. | Agassiz, Poiss. Foss., vol. vii., pi. xxviii. 



\ Eech. Poiss. Foss., vol. iii,, p. 246. § Op. cit., pi. xxx.o, fig. 14. 



