38 MOSASAURUS. 
Little Moreau River, near Fort Pierre. The length of the more perfect is fifteen 
lines, the height twenty lines, and the width twenty-one lines. 
4, A caudal body and a posterior dorsal body, from the forks of Cheyenne River. 
The former possesses rudimental transverse processes projecting from the middle of 
the sides, and measures eighteen lines in length, twenty-one in height, and twenty 
in width. The latter belonged to a very small species, comparatively, or to a very 
young individual of the larger species, but presents no indication of sutural attach- 
ment of parts. It measures fifteen lines in length, sixteen lines high, and nineteen 
lines wide. . 
5. A mutilated posterior dorsal body, and a mutilated anterior caudal body, from 
Little Moreau River, neax Fort Pierre. ‘The former had robust, transverse pro- 
cesses projecting from the middle of the sides of the body anteriorly. Its length 
is thirty-six lines, the height of its posterior convexity thirty-four lines, and its 
width thirty-three lines. The caudal had no chevron bones, but strong transverse 
processes projecting from the lower part of the sides of the body. The articular 
extremities in outline are triangular with strongly rounded angles. The length of 
the body is twenty-eight lines, the height of the posterior convexity about twenty- 
six lines, and the width below twenty-nine lines. 
The vertebra of Mosasaurus, previously mentioned as having been received from 
Dr. Spillman, who discovered them near Columbus, Massie consist of two cer: 
vicals and the fragment of a dorsal. 
The cervical vertebra, represented in Figs. 4, 5, 6, Plate VII, have their body 
twenty-nine lines long, with a transversely oval posterior convexity twenty lines 
wide and sixteen lines high. The spinous process, long, strong, and laterally flat- 
tened, measures about two and a half. inches along its anterior border. ‘The spinal 
canal is about seven lines high and six lines wide. ‘The transverse processes are of 
robust proportions and remarkable form. Springing from the conjunction of the 
vertebral arch and body, they form a rectangular protuberance, at first descending 
upon the side of the latter and then turning forward at a right angle to its anterior 
border. ‘Their upper extremity is thick; and they narrow in their descent and 
anterior extension. ‘Their free extremity presents an L shaped articular surface 
for a cervical rib. The hypapophysis is a strong process projecting downward from 
the back portion of the under side of the body; springing from a carina-like base 
it ends in an ovoid, truncated extremity, as seen in Fig. 4, Plate VII. 
The fragment ‘of a dorsal vertebra, represented in Fig. 7, Plate VII, has the 
body thirty lines in length, and in its details resembles the cervicals just described, 
except that its hypapophysis is a mere rudiment, indicating the position of the 
vertebra to be the next succeeding those anterior dorsals which possess a more 
distinctly developed process of the same character. 
All the vertebrae which I have described or indicated, and indeed all the speci- 
mens I have seen, are apparently complete in their development, that is to say, 
none of them exhibit marks of original separation of the composite elements. 
The union of these in reptiles, especially the complete coossification of the verte- 
bral arch and body, indicates maturity in the skeleton. Never having seen Mosa- 
sauroid vertebre exhibiting certain signs of immaturity I have associated this 
