WILLISTON : NOTES ON SOME EXTINCT REPTILES. 249 



specimen consists of the premaxillo-nasals, maxillary, dentary, 

 splenial, prefrontal, palatine, pterygoids, transverse bones, or- 

 bitosphenoids, atlas, axis, and a number of the bones of the 

 anterior girdle and limbs. The bones are in good preservation, 

 and throw not a little light, not only upon this species, but 

 also upon the genus Clidastes as well. The specimen is large 

 — larger, indeed, than any other Kansas mosasaur except Tylo- 

 saurus dyspdor. It differs from the type specimen in size, but 

 I cannot consider this of specific value yet. The prefrontal 

 bone, while not complete, is of a very different type from that 

 found in the other species of this genus. It has no horizontal 

 plate extending over the orbits, resembling in this respect the 

 same bone in Platecarpvs and Tylosaurus. The teeth in the 

 mandible and maxilla are remarkable for their large and con- 

 spicuous facets, unequaled in any other mosasaur known to me. 

 The pterj-goid has but eight teeth, as in species of Mosasaurus, 

 while the number in all the other known species of Clidastes is 

 from twelve to sixteen. The palatine bone is remarkably small, 

 while the ectopterygoid is large and stout. 



The axis shows scarcely a trace of the zygosphene, but Cope 

 figures it as well developed in the posterior vertebrae. The bones 

 of the paddles are characteristic, as they always are in species 

 of this genus. The coracoid, though incomplete, is evidently 

 emarginate, as in C. velox. This character was unexpected, 

 and tends still further to involve in doubt its value in the sepa- 

 ration of genera. The radius is very broad proximally, and 

 has its two concave borders of nearly equal length, whereas in 

 other forms the radial border is always much the shorter. The 

 ulna is remarkable for its sienderness, resembling a phalanx 

 rather than an epipodial bone. The first bone in the radial side 

 of the carpus, the radial e, has a very narrow free border ; the 

 mediale thus is separated from both the radius and the ulna, 

 which is not the case in any other species of this genus known 

 to me. The first metacarpal also, as usual, is distinctive. The 

 sides are less deeply concave than is usual, and the proximal 

 border is widely expanded. 



Clidastes stenops brings up the question of the generic char- 

 acters of the genus in contrast with those of Mosasaurus. I 

 have been somewhat skeptical of the value of the characters for 

 several years, and the present species makes me more so. There 



