1 90 PALEONTOLOGY 



A symmetrical bone, resembling the episternnm of the Ich- 

 thyosaurus was associated with the preceding remains. It 

 consists of a stem or middle, which gradually thickens to the 

 upper end, where cross pieces are given off at right angles to 

 the stem, and support on each a pretty deep and wide groove 

 indicating strongly the presence of clavicles, and thus pointing 

 out another distinction from crocodiles, in which clavicles are 

 wanting. Most Batrachians possess these bones. 



The modifications of the jaws, and more especially those 

 of the bony palate of the Labyrinthodon leptognathus, prove the 

 fossil to have been essentially Batrachian, but with affinities to 

 the higher Sauria, leading, in the form of skull and the sculp- 

 turing of the cranial bones, to the crocodilian group, in the 

 collocation of the larger fangs at the anterior extremities of 

 the jaws to the Plesiosaurus, and in one part of the dental 

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

 vertebra?, to the Ichthyosaurus. Another marked peculiarity 

 in this fossil is the anchylosis of the base of the teeth to dis- 

 tinct and shallow sockets, by which it is made to resemble the 

 Sphyrama and certain other fishes. From the absence of any 

 trace of excavation at the inner side of the base of the func- 

 tional 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. 



Labyrinthodon pachygnath us. — 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 lower jaw, in addition to the charac- 

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



