LABYBINTH0D0NT1A 191 



L. leptognathus, in the structure of the angular and dentary 

 pieces, shows that the outer wall of the alveolar process is not 

 higher than the inner, as in frogs and toads, the salamanders 

 and menopome, in all of which the base of the teeth is anchy- 

 losed to the inner side of an external alveolar plate. The 

 smaller serial teeth are about forty in number, and gradually 

 diminish in size as they approach both ends, but chiefly so 

 towards the anterior part of the jaw. The sockets are close 

 together, and the alternate ones are empty. The great laniary 

 teeth were apparently three in each symphysis, and the length 

 of the largest was one inch and a half. The base of each tooth 

 is anchylosed to the bottom of its socket, as in scomberoid and 

 sauroid fishes ; but the Lctbyrinthoclon possesses a still more 

 ichthyic character in the continuation of a row of small teeth 

 anterior and external to the two or three larger tusks. The 

 premaxillary bone presents the same peculiar modification as 

 in the higher organized Batrachia, the palatal process of the 

 premaxillary extending beyond the outer plate both externally 

 and, though in a less degree, internally, where it forms part 

 of the boundary of the anterior palatal foramen, whence the 

 outer plate rises in the form of a compressed process from a 

 longitudinal tract in the upper part of the palatal process ; it is 

 here broken off near its margin, and the fractured surface 

 gives the breadth of the base of the outer plate, stamping the 

 fossil with a Batrachian character conspicuous above all the 

 saurian modifications by which the essential nature of the 

 fossil appears at first sight to be masked. 



In the pre-frontal bone there are indications of crocodilian 

 structure. Its superior surface is slightly convex and pitted 

 with irregular impressions ; and from its posterior and outer 

 part it sends downwards a broad and slightly concave process, 

 which appears to be the anterior boundary of the orbit. This 

 process presents near its upper margin a deep pit, from which 

 a groove is continued forwards ; and in the corresponding 



