50 S. W. WILLIS TON 



unless the eggs were very numerous, or unless the young were 

 jealously guarded by the parent, the young reptiles must have 

 stood very little chance in the fierce struggle for existence. 



It is, of course, possible that the shallow waters of the bays 

 and estuaries may have afforded sufficient protection for the young 

 mosasaurs, but this is doubtful, in the entire absence of all 

 remains of such animals in marine deposits. It seems more prob- 

 able that the mosasaurs were brought forth, perhaps alive, in 

 fresh water, that the females ascended the rivers to breed, and 

 that the young remained in such protected places until fairly able 

 to care for themselves. That the mosasaurs, as also the aigial- 

 osaurs, were in part denizens of fresh water may be, perhaps, one 

 reason for the great relative abundance of their remains in the 

 deposits of inland or protected seas. Their occurrence in Kan- 

 sas associated with great numbers of small turtles, pterodactyls, 

 and birds would seem to be fairly good evidence that they were 

 more littoral than pelagic in their habits. 



That mosasaur remains have never been found in fresh-water 

 deposits is not at all conclusive in controversion of this hypoth- 

 esis. We know very little indeed, if anything at all, of the fresh- 

 water life that existed during the times when the mosasaurs 

 flourished. Possibly the Belly River deposits may furnish some 

 evidence bearing on this hypothesis, though I suspect that the 

 mosasaurs had disappeared in America before the time of those 

 deposits. 



It will be of interest to record here certain additional facts 

 concerning the structure of the mosasaurs. A most extraordi- 

 narily complete specimen, referred to Holosaiirus abruptus Marsh, 

 discovered by Mr. E. B. Branson in western Kansas the past 

 summer, has a slight emargination of the coracoids, finally and 

 conclusively demonstrating the invalidity of this character in the 

 separation of the genera. The scales of this form, as apparently 

 also of other species of Platecarpus, are without carina. 



The pubes meet in a perfect symphysis, not as they are always 

 figured in text-books. The ilia were suspended vertically, 

 and the depth of the body posteriorly is greater than the restora- 

 tions indicate. The upper ends of the ilia were in relation, not 



