90 Sir P. Egerton on Fossil Fishes from Southern India. 



period to the Greensand inclusive, the Jurassic species being now separated from 

 Lamna under the generic title of Sphenodus, and from Oxyrhina under that of Me- 

 risfodon. Otodus extends from the Crag to the Greensand, and Corax is restricted 

 to the true chalk. The Ganoid genus Spharodus ranges from the Tertiary beds to 

 the Oolite, and the Cycloid Enchodus is restricted to the chalk. The distribution 

 of species is as follows : — Lamna, 5 tertiary and 1 cretaceous ; Odontaspis, 5 ter- 

 tiary, 4 cretaceous ; Oxyrhina, 1 1 tertiary, 2 cretaceous ; Otodus, 8 tertiary and 5 

 cretaceous ; and Corax, 5 cretaceous. Of the five Placoid genera we have twenty- 

 nine species occurring in the Supercretaceous, and seventeen in the Cretaceous de- 

 posits ; but not a single species has yet been found anterior to the latter period. 

 The evidence, then, afforded by the Pondicherry fishes appears to yield strong cor- 

 roborative testimony to the accuracy of Mr. Forbes's views, derived from the study 

 of the invertebrate remains of the same locality ; and I fully coincide with him in 

 assigning these strata to the Cretaceous period. I am however inclined, consider- 

 ing the number of species collected which must be referred to genera which we 

 know decrease in species as they descend in the stratigraphical scale, from the 

 occurrence also of Maestricht species, and from the presence of the genera Corax 

 and Enchodus not yet found so low as the Neocomian, to place this deposit 

 higher in the system than Mr. Forbes is inclined to do from his investigations. 

 As I have above stated, the Placoid teeth are for the most part mutilated, ren- 

 dering the generic identification a matter of much difficulty and uncertainty, 

 although the specific characters are good and distinct. Agassiz says*, " It fre- 

 quently happens that the root and the lateral cusps are detached from the dental 

 cone, and in this case it is very difficult to distinguish Otodus from Oxyrhina. I 

 shall describe hereafter several species very well characterized, but of which the 

 genus is doubtful, because the perfect root is not known." Again, in prefacing 

 the genus Oxyrhina, he says, " When the base of the root is mutilated, it some- 

 times happens that one is in doubt whether the species belongs to the genus Oxy- 

 rhina, Lamna, or Otodus." He also remarks, after comparing the genus Lamna 

 with Oxyrhina, "The steps from Otodus to Lamna are more gradual, and here 

 we find some species which are actually on the limits between the two genera." 

 Some of the Indian species are in this category, for we find the principal dental 

 cone of the form and aspect of an Otodus associated with the long pointed cylin- 

 drical lateral cusps of an Odontaspis, and the flattened cultriform tooth of an Oxy- 

 rhina furnished with smooth lateral cusps which exclude it from that genus. It is 

 with much hesitation that I have ventured to draw up the following descriptions of 

 the more perfect specimens of the Pondicherry collections, from a consciousness of 

 my own inability to grapple with this most difficult branch of fossil ichthyology, not 



* Poissons Fossiles, vol, iii. p. 266. 



