212 PALAEONTOLOGY. 



The modifications of the jaws, and more especially those of 

 the bony palate, are batrachian : in the collocation of the larger 

 fangs at the anterior extremities of the jaws, there is a resem- 

 blance to the Plesiosaurus ; and in one part of the dental 

 structure, in the form of the episternum, and the bi-concave 

 vertebras, to the Ichthyosaurus. By the anchylosis of the 

 base of the teeth to distinct and shallow sockets, Labyrin- 

 thoclon resembles the Sphyrama and certain other fishes. 

 From the absence of any trace of excavation at the inner 

 side of the base of the functional teeth, or of alveoli of reserve 

 for the successional teeth, it may be concluded that the teeth 

 were reproduced, as in the lower Batrachians and in many 

 fishes, in the soft mucous membrane which covered the 

 alveolar margin, and that they subsequently became fixed 

 to the bone by anchylosis, as in the pike and Lophius. 



Labyrinthoclon joachygnathus. — The remains of this species, 

 which have been obtained, consist of portions of the lower and 

 upper jaws, an anterior frontal bone, a fractured humerus, an 

 ilium with a great part of the acetabulum, the head of a femur, 

 and two ungual phalanges. A portion, nine and a half inches 

 long, of a right ramus of a low r er jaw, in addition to the cha- 

 racters common to it and the fragment of the lower jaw of the 

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

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

 higher than the inner. The smaller serial teeth are about 

 forty in number, and gradually diminish in size as they 

 approach both ends of the row. The sockets are close to- 

 gether, 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 Labyrinthodon 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. 



