524 Mr. Owen on species of 



chiate reptiles. The smooth lateral surface of the vertebral body is not continued 

 in a regular curve to the lower margin of the vertebra, but bends toward that ridge 

 somewhat abruptly at two lines distance from it, as shown in figures 5. and 7. PI, 

 XLV. The present vertebra exhibits the same exceptional condition in the Rep- 

 tilian class as do the vertebrae of existing Batrachians, in having the superior arch 

 or neurapophyses anchylosed with the centrum. The vertebra belongs to the dor- 

 sal series, and from each side of the base of the neural arch there extends obhquely, 

 outwards and upwards, a thick and strong transverse process, the fractured condi- 

 tion of which, on both sides, prevents, however, its length from being ascertained. 

 A very slight ridge ascends from the centrum along each side of the under part of 

 the transverse process ; the two ridges slightly converging and bounding a shallow 

 concavity beneath the transverse process. The upper part of the base of the trans- 

 verse process is continued in an uninterrupted curve into the posterior oblique 

 processes, but it is separated from the anterior ones by a deep oblique and slightly 

 curved fissure. The anterior oblique articular surfaces commence three lines be- 

 hind the articular surface of the body of the vertebra ; they diverge as they pass 

 forward, and thus leave that part of the medullary canal exposed ; the aspect of 

 the articular surface is obliquely upward and inward. The spinous process com- 

 mences at their angle of union, and its base is extended to the corresponding angle 

 of union of the posterior oblique processes, gradually increasing in thickness as it 

 proceeds backwards ; the spinous process was broken off close to its base. The 

 posterior articular processes extend beyond the posterior articular surface of the 

 body of the vertebra as far as the anterior articular surfaces fall short of it ; and 

 they must have covered in the succeeding vertebrae that portion of the spinal canal 

 so left unprotected by its own arch. The spinal canal is slightly expanded at its 

 two extremities, and appears, so far as I have been able to fairly excavate it, to sink 

 in its progress into the substance of the centrum, approaching, as it were, to that 

 peculiar structure which prevails in the still more ancient reptiles of the magnesian 

 conglomerate. The strength and direction of the transverse processes indicate an 

 expanded respiratory cavity protected by ribs. 



Episternum. — A symmetrical bone, most resembling the episternum of the Ichthyo- 

 saurus, but with the median piece broader, flatter and thinner, so nearly corresponds 

 in its proportions with the preceding vertebra that I here describe it, as belonging 

 very probably to the Labyrinthodon leptognathus (PI. XLV. figg. 9 and 10). The 

 stem, or middle piece of this bone diminishes to a mere plate or film below, and 

 thickens towards the upper end where the cross-pieces are given off, and these pass 

 outwardly at right angles to the median stem and support, each, a pretty deep and 

 wide groove, contracting to a point at the upper part of the median stem : these 

 grooves indicate strongly the presence of clavicles, which are wanting in the Cro- 

 codiles, where the sternum or episternum presents only its median piece, with 



