ITS STRUCTURE, BULK, AND ASPECT. 81 



were certain curious irregularities of dentition in the Aster- 

 oUpis, which seemed to have had a considerable range, and 

 which make the jaws of one individual differ a good deal in 

 appearance from those of another of the same species. In 

 some specimens we see recipient pits or sockets that have no 

 reptile teeth growing up beside them ; while in others, the 

 too wide socket, one-half of which usually remains a recipient 

 pit, we find occupied to the full by a second tooth, growing 

 up so close beside the ordinary one, that their points stand 

 scarce a line apart. The double tooth formed in this manner, 

 when, as in the figured specimen (fig. 36), unaccompanied by 

 Fig. 36. 



UNDER JAW OF YOUNG ASTEROLEPIS (INNER SIDE). 



(Nearly nat. size.^ 



a recipient pit, must have been accommodated in the oppo- 

 site jaw by a recipient pit unaccompanied by a tooth ; and 

 thus the pit without tooth and the double tooth without pit 

 were answering and mutually accommodating irregularities. 

 There are instances, however, in which the double tooth had 



of apparent socket ; and a reptilian relationship has been deduced from 

 this peculiarity. The deduction, however, though apparently just, would 

 be perhaps more direct were it founded rather on the existence of the re- 

 cipient hollow, than of the socket beside the hollow ; for the depth of 

 the socket seems to have been dependent on the depth of the hollow, and 

 proportioned to it. If the reptile tooth rose high over the edge of the 

 jaw in which it was placed, it was necessary that the recipient hollow in 

 the opposite jaw should be correspondingly deep, — just as a long sword 

 requires a deep scabbard to sheath it in ; and if the hollow was deep, the 

 socket of the tooth that stood up beside it, and whose base descended to 

 ita level, had to be correspondingly deep also. 



F 



