TRIASSIC LABYRINTHODONS. 193 



vacant sockets between the teeth in place show more or less advanced beginnings 

 oE successional teeth. The figures of the mandible and teeth are of the natural 



size. 



Vertebrce of Labyrinthodon. (Batrachia, Plate 5.) 



The proportions of a vertebral fragment, associated with the above-described 

 mandible, in the Trias of Coton End, lead me to refer it to the species pachy- 

 gnathus. Fig. 1, showing a portion of the fore articular surf ace of the centrum , 

 with the coalesced base of the neural arch, gives the moderately concave character 

 of that surface. The upper view of the same vertebral fragment (fig. 2) 

 determines the fore and hind ends by the bases of the zygapophyses of the 

 coalesced neural arch fortunately remaining. The base of a broad, depressed 

 diapophysis is also shown, and is further exemplified in the side view (fig. 4). The 

 hind articular surface of the centrum has suffered fracture, forbidding determina- 

 tion of its natural shape. The minutely cellular, almost compact, texture of the 

 bone is displayed by the fractured surface in fig. 3. 



A better preserved vertebra, in size referable to Labtjrinthodon leptognatlms, 

 affords the subjects of figs, 5—8. The degree of concavity of the fore surface is 

 shown in fig. 7, in which the centrum is associated with so much of the neural 

 arch as exhibits the position and shape of the prezygapophyses which received the 

 articular ends of the postzygapophyses, unfortunately mutilated, with the corre- 

 sponding articular surface of the centrum, as shown in fig. 8, In the characters 

 of the vertebra from a part of the trunk, as exemplified in the specimens from 

 two of the British species of the present singular genus, we find the Labyrinthodon 

 superadding modifications to the vertebrae of the highest existing Batrachia (toads, 

 frogs, salamanders), which, as in the dental and osteological characters next to be 

 noticed, manifest an association of Reptilian (Crocodilian, Dinosaurian) features 

 with an essentially Batrachian organisation. The portions of ribs which have 

 been recovered show these bones to have been of greater relative length and 

 curvature than in any existing Batrachians, and in the character of size they accord 

 with that of the articular process and surface developed from the neural arch. 



The subject of figs. 9 and 10, in Plate 5, might well have been interpreted, if 

 found alone, as evidence of an extinct Reptile of higher grade than a salamander, — 

 to an Icthyosaur, for example. It is plainly a sternal bone, showing articidar 

 concavities for a pair of clavicles ; or it may answer to that part of the complex 

 scapular arch in Reptiles which has been named " episternum." The locality of 

 the fossil and its associations with unquestionable remains of Labyrinthodont 

 reptiles support its reference to that genus ; and, from its size, to the species 

 leptognatlms. The stem or body of the bone thins off as it recedes fi'om the 

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