156 University of Kansas Geological Survey. 



tal carpal, and with the first and second distal carpals. The 

 middle one articulates with the mediale, the other two of the 

 distal row, and the third metacarpal. The outer one articulates 

 with the radiale, the mediale, the middle distal carpal, and the 

 fourth metacarpal. These three bones are thinner than the 

 others, save the mediale. 



Platecarpus. The carpal bones of Platecarpus are four in num- 

 ber, articulating rather closely together, and situated on the ul- 

 nar side of the wrist. They are the ulnare and mediale of 

 the proximal row, the first and second of the distal row. The 

 radiale, pisiform and outer distal carpal are wanting. This 

 structure in connection with the absence of the condylar proc- 

 ess of the distal extremity of the radius and the much weaker 

 first digit, shows a decided inferiority in this part of the pad- 

 dle as compared with Mosasaurus and Clidastes. The ulnare, 

 the largest, articulates with the ulna, fifth metacarpal, and the 

 other three carpals. The mediale articulates with the ulnare, 

 radius, and outer distal carpal. The two distal carpals articu- 

 late with the second and third metacarpals respectively. 



Tylosaurus. In Tylosaurus there is but a single carpal, a small, 

 rounded bone, situated opposite the end of the ulna, and doubt- 

 less corresponding to the ulnare. It does not articulate with 

 any bone, but was surrounded on all sides by cartilage. 



Metacarpals. 



Clidastes velox. Of the five metacarpals in Clidastes, the first 

 is the broadest, the fifth the shortest, and both much flattened. 

 The other three are more slender, with expanded extremities 

 and constricted shaft. The first is much expanded on the 

 proximal extremity, the broadly convex end articulating with 

 the radiale, and, together with the next three, permitting very 

 free lateral movement. The distal extremity is less expanded 

 than the proximal, the end squarely truncate for close union 

 with the phalanx. The inner border, thicker than the outer, 

 has a shape somewhat like a fish-hook, terminating in an 

 acute distal angle of the bone. The outer border is much 

 shorter and has a slight convexity at the bottom of the con 



