18 HYPOSAURUS. 
dentinal substance. The base of the crown is excavated. The length of the 
specimen is fourteen lines and a half; its diameter at base, six lines. 
The second specimen, Fig. 23, differs from the former in being somewhat curved, 
elliptical in transverse section, and in the fluting extending to the bottom of the 
crown. The apex is worn off, and the specimen in its present state is ten lines 
and a half long, by six lines and a half in diameter antero-posteriorly near the base. 
The two teeth differ from those of Pliogonodon, probably also from the Green- 
sand of North Carolina, in which the crown is proportionately longer, and has its 
surfaces subdivided into narrow planes and provided with a few interrupted vertical 
plice. They differ also from those of Polygonodon, in which the crown of the tooth 
is long and narrow and its surfaces subdivided into planes without folds or strie. 
Dr. Emmons, in his Report of the North Carolina Geological Survey, page 219, 
fig. 38, has described and figured a large Crocodilian tooth, obtained from a bed of 
Miocene marl, at Elizabethtown, Bladen County, N. C. The tooth, together with 
some bones, Dr. Emmons nevertheless thinks originally belonged to the Green-sand 
formation beneath. It has a conical crown, and a robust cylindrical fang ; is hollow, 
and moderately curved. ‘The crown is described as circular in transverse section, 
and without carinz, or acute ridges separating the inner and outer surfaces, the 
enamel of which is traversed with “irregular rugose ridges.” .The specimen is 
referred to the genus Polyptychodon, under the name of P. rugosus. 
Another tooth, found with the preceding, described and figured in the same 
chapter, page 220, fig. 39, and referred by Dr. Emmons to the same animal, appears 
rather to have belonged to Mosasaurus. 
Fig. 12, Plate VIII, represents a dermal plate, which, together with a small 
fragment of a jaw, and the mutilated crown of a tooth, were submitted to my 
examinatiom from the Burlington County Lyceum of Natural History. The dermal 
plate measures two inches by twenty lines, and is without a carina. The fragment 
of jaw, much mutilated, is two and a half inches long, straight, and contains the 
much curved fangs of two teeth. It indicates a small species of Gavial, or perhaps 
belonged to the young of T'horacosaurus Neocesariensis. The isolated crown of a 
tooth closely resembles that of Fig. 7, Plate I, but is rather more curved. 
HYPOSAURUS. 
Hyposaurus Rogersii. 
Hyposaurus Rogersii, OwEN, Quart. Jour. Geol. Soc. Lond. V, 1849, 380, pl. xi, figs. 7-10. 
Holcodus acutidens, GieBEs (in part), Mem. on Mosasaurus, &c., Smithsonian Contrib. II, 1850, 9, pl. iii, fig. 13 
Among the fossil vertebra, from the Green-sand formation of New Jersey, de- 
scribed by Prof. Owen, in the Journal of the Geological Society of London, were 
two specimens with biconcave bodies, which are referred to a genus of the Croco- 
dilian family under the name of Hyposaurus Rogersii. Prof. Owen remarks that 
“the peculiar and distinctive character of these vertebre is shown in the large size 
and especially the great antero-posterior extent of the hypapophysis. Its base 
occupies the whole extent of the median line of the inferior surface between the 
prominent borders of the anterior and posterior articular ends of the centrum.” 
