Page:Synopsis of the Exinct Batrachia and Reptilia of North America. Part 1..pdf/48

44 green sand of New Jersey, described previously in the Proceedings of the Academy of Natural Sciences, but in that the large transverse process is cylindrical, while it is compressed cylindroid in the Ark. saurian, and probably the latter belongs to a distinct genus, for which the name is proposed. The bones are in a hard  with, and they probably belong to the cretaceous or to the  period. One of the most perfect of the vertebra) presents the following measurements:

Inches.

Dr. Leidy proposes to consider this species as the type of a genus distinct from the present, because its diapophyses are compressed in section, while those of Cimoliasaurus arc cylindroid. I think this difference depends on the position in the vertebral column. These processes descend on the anterior part of the column and become more flattened, until they resemble diapophyses of ordinary cervicals. This vertebra therefore was an anterior dorsal.

Leconte's notes on Geology of the route of the, 1868, p. 68. Cope, Proceed. Acad. Nat. Sciences, 1868, p. 92.

This has been more completely preserved to us than any other American representative of the order, and hence may be accepted as most clearly expressive of its characters. In the interpretation of these, however, considerable difficulty has been experienced, as the structure form appears, at first sight, to reverse to a remarkable degree, the usual proportions of known.

The determination of the extremity of the  has been rendered certain by the fortunate completeness of the cervical series, as the extraordinary length of the latter, equalling three times that of the body, renders the most careful scrutiny necessary.

The are every where continuous with the centra, without sign of suture, and are externally plane. The is exceedingly small for the size of the, especially on the s and s.

The dorsal vertebrae are remarkable from the fact that the disappear on the anterior part of the series, and gradually diminish in length from behind forwards to the point of disappearance. On the and posterior parts of the series they are very elongate, and rise for a short distance from the basis of the neural arch. , they descend and shorten, and finally remain only as the slightly elevated borders of rib-pits. Throughout the whole of the anterior portion of the column to the cervicals, the neural spines are of great elevation, and of such extent as to be nearly continuous.

The vertebræ are not only more numerous, but become anteriorly much smaller and more attenuated than in its allies of the same family. They are remarkably corn-