ON BRITISH FOSSIL REPTILES. 185 



are long and slender, gradually diminishing in size towards the anterior portion 

 of the jaw, and the fragment presents a linear series of not less than fifty 

 sockets, placed alternately a little more internally ; and at the anterior in- 

 flected part of the jaw is the base of the socket of a large tooth. The ante- 

 rior portion of the jaw being broken off', it is uncertain if the serial teeth were 

 continued externally to the anterior tusk, which is a remarkable ichthyoid 

 character noticed in another species of Lahyrinthodon. 



The sockets of the teeth are shallower than in the upper jaw ; the outer wall 

 is more developed than the inner, and the anchylosed bases of the teeth more 

 nearly resemble, in their oblique position, those of existing Batrachia. With 

 regard to the modification of the microscopic structure of the teeth, I may ob- 

 serve that, between the apex and the part where the inflected vertical folds of 

 the cement commence, the tooth resembles, in the simplicity of its intimate 

 structure, that of the entire tooth of ordinary Batrachia and most reptiles ; 

 and in the lower or basal half of the tooth the structure described in the works 

 before quoted commences, and gradually increases in complexity. 



From the long and slender character of this ramus, the length of the head, 

 as compared with the breadth, approximates more nearly to Crocodilian pro- 

 portions than to tlie ordinary Batrachian ones ; but among existing Batrachia 

 it resembles most nearly the Amphiume. 



A dorsal vertebra from Coton End presents further evidence of the Batra- 

 chian nature of the Lahyrinthodon. It has concave articular cavities at the 

 extremities of the body, a condition now known, among existing reptiles, only 

 in the Geckos, and in the lower or perennibranchiate division of Batrachians. 

 It is a common structure in extinct Saurians, but the depth of the vertebral 

 articular cavities in the Lahyrinthodon exceeds that in the Amphiccelian Cro- 

 codilians and in most Plesiosaurs. The body of the vertebra is elongate and 

 subcompressed, with a smooth but not regularly curved lateral surface, termi- 

 nating below in a slightly produced, longitudinal, median ridge ; and it ex- 

 hibits the same exceptional condition in the Reptilian class as do the vertebrae 

 of existing Batrachians, in having the superior arch or neurapophysis anchy- 

 losed with the centrum. From each side of the base of the neural arch a thick 

 and strong transverse process extends obliquely outwards and upwards. 



A symmetrical bone, resembling the episternum of the Ichthyosaurus, 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 indi- 

 cating strongly the presence of clavicles, and thus pointing out another di- 

 stinction 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 Lahyrinthodon leptognathus, prove the fossil to have been essentially 

 Batrachian, but with affinities to the higher Sauria, leading, in the form of the 

 skull and the sculpturing of the cranial bones, to the Crocodilian group, in 

 the collocation of the larger fangs at the anterior extremities of the jav's to 

 the Plesiosaurus, and in one part of the dental structure, in the form of the 

 episternum, and the biconcave vertebra;, to the Ichthyosatiriis. Another 

 marked peculiarity in this fossil is the anchylosis of the base of the teeth to 

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

 aiul certain other fishes. From the absence of any trace of excavation at the 

 iimer 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 iu 

 the lower Batrachians and in many fishes, especially the higher Chondroptery- 

 gii, which formed t\ia Am jjhibia Nantes of Linnaius, in the soft nmcous mem- 

 brane which covered the alveolar margin, and that they subsequently became 



