38 FOSSIL REPTILIA OF THE 



compressed, and terminates in a slightly convex, thick, smooth articular border. 

 Nine or ten inches below this, the shaft, slightly increasing in breadth and decreasing 

 in thickness, presents a thick, rough, and prominent ridge, three inches and a half in 

 length, apparently for the attachment of some strong muscle ; behind this ridge the 

 shaft contracts to a diameter of one inch nine lines, and to a circumference of four 

 inches six lines. At ten inches from the distal end it increases in thickness, assumes 

 a trihedral form, with one edge produced and convex, subsiding above the articular 

 end, which is in the form of a simple convex condyle, not excavated for a trochlear 

 joint in the middle, but with an irregular branched impression or smooth groove at 

 that part : the articular surface extends upon the fore and the back part of the shaft, 

 about two inches six lines from the end, contracting posteriorly, and with a convex 

 border anteriorly above, where there is a shallow semilunar depression. There is a 

 very deep large hemispheric pit on each side above this condyle. There is no 

 medullary cavity in this bone. 



These two long bones are more like the tibia and fibula of the larger lizards than 

 the radius and ulna : there can be little doubt that they belong either to the leg or to 

 the antibrachium, but they differ too much in shape from any of the bones of those 

 segments in the larger lizards, with which I have been able to compare them, to 

 encourage me to hazard a positive determination. I should be disposed to ascribe 

 them, from their length and slenderness, to the hind leg. They are more Lacertian 

 than Crocodilian in their general character ; and they belong with great probability to 

 the Mosasaiirus. 



A metacarpal or metatarsal bone of the same reptile gives the following 

 dimensions : — 



Feet. Inches. 



Extreme length . 1 8 



Extreme breadth of the broader articulating surface or upper end 4| 



Central depth of ditto 3| 



Breadth of lower end . 3 



The proximal or upper end is suddenly expanded, with an undulated or parti 

 convex partly concave articular surface, nearly flat, at right angles to the shaft ; sub- 

 triangular with the angles rounded off, or reniform on account of the deep notch 

 posteriorly, below which there is a depression. A ridge is continued from the shaft 

 upon two of the angles, which gives a subhemispheric section of the shaft at six 

 inches from the head. Here a medullary cavity nine lines in diameter is exposed. 

 One half of the parietes of the middle third of the shaft of this bone is preserved, 

 which shows a continuation of the medullary cavity and the development of an 

 angular ridge from the shaft, which subsides about six inches from the distal end. 

 This end slightly expands into a simple convex condyle, with the articular surface 



