MOSASAURUS. 45 
deposits of Nebraska, is represented in Fig. 6, Plate VIII, and may, perhaps, apper- 
tain to a young Mosasaurus. It resembles a radius or tibia of Plesiosawrus. It is 
much compressed, cylindroid in form, and expanded nearly equally towards the 
extremities. The articular surfaces are transversely elliptical, slightly convex, and 
roughened for the attachment of cartilage. The measurements of the specimen 
are as follows :— 
Inches. Lines. 
Length ; : - - - - : : : - S se 8 
Breadth at middle of shaft . E A : : : ; P ea | 1 
Thickness at middle of shaft ‘ : 5 5 ° ; 6 
Breadth at extremities . : = : . ° é j . all 8 
Thickness . : ‘ : ‘ : ; P A ; : 9 
An isolated bone, obtained by Dr. Spillman, from the same formation, which 
contained the humerus and other bones previously described, is represented in Fig. 
7, Plate VIII... It resembles the preceding specimen suspected to be a radius or 
tibia of a young Mosasaurus, but is much less compressed, and its articular surfaces 
are nearly plane or slightly concave. Its measurements are as follows :— 
Inches. Lines. 
Length : : C : : : : c : . : . 2 
Breadth at middle of shaft 3 : . 4 : : s : 9 
Thickness at middle of shaft ; ; ; : 3 . 4 : 7 
Breadth of proximalend . ; : ; : : 5 A 5! 6 
Thickness of proximal end : ; : ; : : ee 
Breadth of distal end A 2 5 : 6 ‘ : 5 el 4 
Thickness of distal end i! ‘3 S : rs : 3 5 4 10 
A carpal bone, represented in Fig. 8, Plate VIII, found by Dr. Hayden on the 
Big Cheyenne River, probably belongs to Mosasawrus. 'The specimen is hexagonal 
at the border, and has its broad surfaces moderately concave. Its greatest breadth 
is one inch, its shortest ten lines; its thickness ranges between three and five lines. 
An undetermined reptile bone, accompanying the latter, is represented in Fig. 
10, of the same Plate. It is a short, much flattened, cylindroid bone, constricted 
at the middle, where it measures one inch and a quarter wide, and three-quarters 
of an inch thick. The upper extremity expands into a broad, flat, circular articular 
surface, with a narrow oblique prolongation at one side. The surface is broken off 
at the opposite side, but independent of the prolongation it measures about ane 
inch and a quarter in diameter. The lower extremity expands into a transversely 
semi-circular, ellipsoidal articular surface, measuring two inches and three-quarters 
in its long diameter and ten lines in its short diameter. ‘The length of the bone is 
one inch and three-quarters. 
Another undetermined reptile bone, represented in Fig. 9, Plate VIII, belonging 
to Prof. James Hall, was found by Messrs. Meek and Hayden, among loose frag- 
ments at the base of a Cretaceous bluff, five miles below Daurion’s Hill, Nebraska. 
The bone is a little over two inches in length, and somewhat resembles the preced- 
ing, but appears lengthened at the expense of the breadth. The shaft at middle 
is eleven lines wide and eight lines thick, and is ovate in transverse section, The 
upper extremity expands into a flat, nearly circular articular surface, about one inch 
