396 O. C. Marsh on new Mosasauroid Reptiles, etc. 
descends vertically from the posterior part of the centrum, re- 
sembling strongly the hypapophyses of the medial trunk verte- 
bree of the constricting snakes, especially the Eocene Paleophis, 
which may, perhaps, yet prove to bea sapere of some of 
the Mosasauroids. The present genus a s to have its near- 
est allies in Macrosaurus and Clidastes, es Me the former, 
which has, however, the dorsal vertebree more or less compresse 
From the latter genus it may readily be distinguished by the 
absence of the zygosphenal articulation. 
e remains on which the species is founded consist of a 
posterior cervical, and an anterior dorsal vertebra; the right 
splenial bone with its concave articular face, and a small por- 
tion of the base of the skull. A coracoid found near these 
specimens probably belonged to the same animal, although it is 
smaller than the other parts of the skeleton would apparently 
indicate, and differs considerably in form and proportions from 
the corresponding bone in both Macrosaurus ot Clidastes. The 
splenial bone differs from that of Mosasaurus in the form of its 
articular face, and in being more overlapped in front of the 
joint by the dentary. The dimensions of the posterior cervical 
vertebra are as follows :— 
a of centrum below, --..--..--- 2 inches, . “rte 
Transverse diameter of articular oupy..: 1 
Vertical diameter of articular cup, ---- ne : 
Distance from center of cup to middle of 
lateral edge st Reda 
ne of diapophyses below lower mar- } 
56 * 
Length. of panos below lower 
Wate Of bila: os is cin wise erect 
The dorsal ee has no trace of a hypapophysis, and the — 
lower surface of the centrum is remarkably flat. ‘The anterior — 
downward prolongation of the diapophyses still project below 
the centrum, but they have become o processes, Pp Ag 
separated from the more vertical portion of the dia ophyses by ¢ : 
notch. The following are the more important enslons 0 
this vertebra :— 
- Length of centrum below, --.-------- . seer 3 ines. 
Transverse diameter of cup, 
Vertical diameter of cup, ; “ss 
Width of neural canal slow tc aces 
Width oo extremities of anterior ook 
ZY. gapop hyses, Pee Oe ee s : 
Length of oe below lower sur- 
face of cen - 
These remains, wie were einaentt discovered b Ne Mr. ey, 
ersey, 
in the lower Cretaceous Marl bed at Hornerstown, 
bai 
