200 University of Kansas Geological Survey. 



relative to age. ... In this view of the case, some of the 

 many species of Mosasauroids may have been founded on differ- 

 ent ages of the same." 



This statement I can corroborate. I have seen altogether not 

 far from 2000 specimens of Mosasaurs, and have collected with 

 my own hands not less than 400. But I have- never seen one 

 that could unhesitatingly be pronounced to be that of a young 

 animal. And certainly the Mosasaurs did not all die of old age. 

 One suspects the youth in some cases from the distorted condi- 

 tion of the bones, due probably to less well-ossified conditions. 

 The neural sutures are never found unclosed, and rarely do we 

 find the bones of the skull macerated and separated. It is cer- 

 tain, then, that size cannot have a very great specific value. 



The smallest specimen of a Mosasaur in our collection has the 

 mandibles 250 mm. in length ; that is, indicating an animal a 

 little over six feet in length. These mandibles are more slender 

 than are those of the specimen of C. velox used for description, 

 but no more slender than in another specimen of larger size 

 that should be referred to C. velox. In this specimen the jaws 

 have a length of 365 mm. In the smallest specimen the coro- 

 noid projects much beyond the proximal end of the presplenial, 

 while in all the other specimens the dentary projects much 

 further back. 



Marsh has given certain characters for the quadrate of C. 

 pumilus which do not exist in the smallest specimen under ex- 

 amination. The quadrates in this specimen measure but thirty- 

 three mm. in length, with the distal articular face twenty mm. in 

 extent, precisely that of the type. The two quadrates agree 

 exactly with those of the velo.r described in the foregoing pages, 

 and C. velox has perhaps the most characteristic quadrate of any 

 species of the genus. The inner face is not concave longitudin- 

 ally on the anterior border, as it is in all those that I know of or 

 that have been figured, but is nearly straight. The sharp ridge 

 beginning just below and to the anterior side of the stapedial 

 pit and extending towards or to the anterior inferior angle is 

 present, and always wanting in the quadrate of the other spe- 

 cies. Just anterior to the pit, on the border, there is a small 



