1844.] 383 



the root and the lateral cnsps are (ietached 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 

 characterised, but of which the genus is doubtful, because the 

 perfect root is not known." Again, in prefacing the genus Oxy- 

 rhina, 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 Oxyrhina, Lamna, or Otodus." He also remarks, after 

 comparing the genus Lamna with Oxyrhina, " The steps fi-om 

 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 cylindrical lateral cusps of an Odontaspis, and the 

 flattened cultriform tooth of an Oxyrhina 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 descrip- 

 tions 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 unmixed with doubts of 

 the stability of the generic and specific characters as at present 

 acknowledged in the " Poissons Fossiles." Agassiz has himself 

 complained of the paucity of materials for arriving at any very 

 definite conclusions as to the variations of form in the teeth occur- 

 ring in the various positions in the mouth of the same species. 

 Those naturalists who have studied the recent sharks are well 

 aware of the extent of those variations in a single individual, and 

 can, therefore, appreciate the difficulties under which Agassiz has 

 laboured in attempting a systematic arrangement of the fossil 

 Squaloids. As I am in hopes this distinguished Ichthyologist will 

 shortly have an opportunity of examining the Indian collections, I 

 offer the following descriptions as provisional rather than final ; or, 

 at all events, as giving the characters of forms in themselves 

 distinct, but which may hereafter be grouped together under legi- 

 timate generic and specific denominations. 



Cycloid Order. 



Scomheroid Family. 



Enchodus serratus Eg. — Three teeth from the Pondicherry 

 beds, evidently belonging to the genus Enchodus. As I have 

 before stated, they bear a very close resemblance to the species 

 figured by Agassiz as Enchodus halocyon ; at the same time 

 (although the materials are too defective to warrant any definite 

 conclusion), there are appreciable discrepancies of sufficient im- 

 portance to induce me to abstain from identifying the Indian teeth 

 with the species alluded to. The most perfect specimen, as com- 

 pared with teeth of similar size of E. halocyon, presents the follow- 



