102 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 7, 



fossils (see PI. IV. 5, 6). In this point of view the dorsal aspect of 

 the vertebra is of a subquadrangular form ; the articulating planes of 

 the zygapophyses are horizontal ; the neural arch rises into a roof or 

 dome, the spinous process forming only a slight ridge, and not a 

 sharp crest, as in Lizards*. The body or centrum of the vertebra is 

 cylindrical, slightly contracted in the middle, and both articular ends 

 are concave : such at least is the inference I have drawn, after a careful 

 consideration of the various appearances presented by the fragmentary 

 remains of the spinal elements. If this view be correct, the characters 

 of the vertebrae are peculiar: the centrum resembles that of the 

 vertebrae in the Axolotl, and in numerous extinct Saurians, while the 

 neural arch approaches the corresponding element in the Salamanders. 

 A comparison of PI. IV. 6, which is an enlarged view of the dorsal 

 aspect of the neurapophysis of one of the fossil vertebrae, with the 

 vertebra of the large Salamander, Sieboldtia maxima (PI. IV. 7), for 

 which I am indebted to J. E, Gray, Esq., shows this resemblance. 

 Another remarkable feature of the spinal column in the fossil reptile 

 is the great uniformity of character in the vertebrae throughout the 

 spine. The sacral vertebrae are but indistinctly denoted : the caudals 

 have long apophyses, and only ten or twelve vertebrae are disclosed, 

 the terminal series being concealed beneath the stone ; probably the 

 entire length of the tail did not exceed an inch and a half. 



Ribs. — The ribs, of which there are twenty-four pairs, are remark- 

 ably slender, and appear to have been attached by a simple head as 

 in the Lizards ; but, as only imprints of these processes remain, the 

 mode of union with the bodies or neural arches of the vertebrae is 

 not distinctly recognizable. Some of the impressions seem to indicate 

 that the ribs were attached to a tubercle on the anterior part of the 

 centrum : others may be traced to the middle, as if occupying the 

 same relative position as in the Salamanders (see PL IV. 7) ; but the 

 evidence on this point is very equivocal. 



The length and -curvature of the costal processes and the simple 

 mode of attachment are lacertian characters, and strongly contrast 

 with the usual abbreviated and rudimentary condition of the ribs in 

 Batrachians ; yet there is no proof that any of these processes extended 

 forward to the sternum, or were united to thoracic or abdominal car- 

 tilages ; on the contrary, the extremity of each rib appears to be 

 entire, as if none of these bones were originally prolonged beyond 

 the impressions left on the stone (PL IV. 9) ; and should future 

 discoveries confirm the view above enunciated of the structure of the 

 neural arch, it may be well to remind the reader, that in a genus of 

 living batrachians, the Pleurodelesf, the ribs are developed almost to 

 as great an extent as in this fossil reptile :|:. 



Pelvis. — On the specimen, PL IV. 9, the form of this part of 



* In Lizards, after the twelfth dorsal vertebra the spinous process is a strong, 

 well-marked character. — Cuvier. 



t Pleurodeles, Waltl, Gray's Catalogue of Amphibia in the British Museum, 

 p. 17. 



J I am indebted to the eminent zoologist of the British Museum, John Edward 

 Gray, Esq., for this reference ; and also for unrestricted access to the important 

 osteological collection which has been formed by his exertions. 



