Apr. 1903. North American Plesiosaurs — Williston. 77 



hypothesis that they were swallowed by the animal with food, as is 

 the case with several living reptiles and birds. If this view should be 

 Inlcl admissible, it would suggest that, as the teeth were too small 

 for anything but prehension, a structure analogous to a gizzard or the 

 stomach of an edentate, may have used these pebbles to assist in 

 breaking up or crushing the food on which the saurian lived."' 



