MOSASAURTJS. 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 Plesiosaurus. 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 foUows : — 



Inches. Lines. 



Length 2 8 



Breadth at middle of shaft 1 1 



Thickness at middle of shaft 6 



Breadth at extremities .......... 1 8 



Thickness 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 2 



Breadth at middle of shaft 9 



Thickness at middle of shaft t 



Breadth of proximal end 1 6 



Thickness of proximal end 1 



Breadth of distal end 1 4 



Thickness of distal end . 10 



A carpal bone, represented in Fig. 8, Plate VIII, found by Dr. Hayden on the 

 Big Cheyenne Eiver, probably belongs to Mosasaurus. 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, cyhndroid 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 ofi" 

 at the opposite side, but independent of the prolongation it measures about one 

 inch and a quarter in diameter. The lower extremity expands into a transversely 

 semi-oircular, 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 HaU, was found by Messrs. Meek and Hayden, among loose frag- 

 ments at the base of a Cretaceous blufi", 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 



