OF THE NEW RED SANDSTONE FORMATION OF PENNSYLVANIA. 199 



CLEPSYSAURUS PENNSYLVANICUS, Lea. 



Vertebra. Natural size. PL 17, fi^. 1 and 2. PI. 18, fi^. 2, 3, 4 and 5. PI. 19, fio-. 2. 



The vertebrae belong to the bi-concave system. All the specimens are more or less 

 mutilated, eroded, crushed, or bruised, so that it is quite impossible to assign their par- 

 ticular position in the vertebral column. It is evident that they are more compressed 

 laterally than vertically (see pi. 17, fig. 2,) and in one of the specimens where three of 

 the vertebrae are in juxta position, they are but slightly compressed, (pi. 18, fig. 5.) 

 The superior portion of all the three is broken off, and none of the processes remain 

 attached, to designate what portion of the column they belonged to. The spinal canal 

 is not perfect in a single vertebra. In two broken specimens of the centrum, there is 

 a slight appearance of this canal, having the character described by Dr. Riley and 

 Mr. Stutchbury* in the Thecodontosaurus of the Magnesian Limestone of Bristol f 

 They say, " The body of the vertebrse is hollowed out by a deep and narrow depres- 

 sion on its upper surface, so that the inferior boundary of the vertebral canal would 

 not be on one level plane, as in other animals, but would present a succession of 

 narrow and deep depressions, corresponding to the body of each vertebra." (p. 353.) 

 Such, no doubt, has been the case in the spinal canal of our animal, and it presents 

 a characteristic so peculiar, and so important, as to deserve particular attention. The 

 form of the spinal canal is, I believe, without any analogy in the vertebrata of more 

 recent formations, and therefore this peculiar structure is of the highest importance 

 in the consideration of the position of this rock, as it is also in comparative osteology. 

 The enlargement of the spinal canal in the middle of the centrum, is characteristic in 

 these reptiles. It is evident that at the junction of each vertebra,the canal must 

 present a node of more or less magnitude. 



Great consideration is also due to the fact of the centrum being concave, both 

 posteriorly and anteriorly. Dr. Riley and Mr. Stutchbury describe the vertebrse of 

 their reptile as being " concave at each end." M. D'Orbigny states that among the 

 extinct reptiles there are six genera which had bi-concave vertebrae. f The former 

 gentlemen very properly remark, thatth'e leading characters of these vertebrae are the 

 double cancave system; the hour glass form of the annular portion, and the peculiar 

 form of the vertebral canal. 



* Geological Society's Transactions, v. 5, 2d ser., p. 352. 



+ Dr. Riley and Mr. Stutchbury founded the genera Paloeosaums and Thecodontosaui'us on the character of the 

 teeth. The bones not being found in connexion with the teeth, they hesitated to assign them to either of the 

 genera which they established. They describe the vertebrae " as possessing the peculiar characters of having 

 the centre of the body diminished one-half in its transverse and vertical diameters, so as to resemble an hour- 

 glass, ; of a suture connecting the annular part or body with the processes ; and in the extremities of the vertebrae 

 being deeply concave. These characters, the authors conceive, distinguish the fossil vertebrae from those of all 

 recent Saurians." Proceedings Geological Society, v. 11, p. 399. 



J Cours Elementaire, p. 205. 



