OF THE NEW RED SANDSTONE FORMATION OF PENNSYLVANIA. 
17 
CLEPSYSAURUS PENNSYLVANICUS, Lea. 
Vertebra. Natural size. PI. 17, fig. I and 2. PI. 18, fig. 2, 3, 4 and 5. PI. 19, fig. 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 vertebrae 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 osteologv. 
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 vertebrae 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.The former 
gentlemen very properly remark, that the 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. 
-j- Dr. Riley and Mr. Stutchbury founded the genera Palceosaurus and Thecodontosaurus 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. 
I Cours Elementaire, p. 205. 
