76 Field Columbian Museum — Geology, Vol. II. 



never expect to find plesiosaur coprolites containing undigested 

 remains of bones or other solid material. 



The nearest place where the animal could have found such 

 pebbles on the sea beaches must have been several hundred miles 

 away from Ellsworth, where the animal finally perished. We may 

 conclude, hence, that the plesiosaurs were roving animals. 



Since the discovery of this specimen two others with siliceous 

 pebbles have been received at the Kansas University museum, one 

 from the Niobrara of Kansas and the other from the Comanche Cre- 

 taceous of Clark County, Kansas (PI. XXIX.) In neither of these 

 cases were the pebbles worn into such regular figures as in the 

 Benton specimen, and all the pebbles were dark in color, none of 

 them quartzite. 



What the use of these pebbles was I will not venture to say. 

 They may have .served as a sort of weight to regulate the specific 

 gravity of the animals, or they may have been swallowed accidentally. 

 If, as I believe probable, the plesiosaurs were in the habit of feeding 

 upon invertebrate animals, seeking such in the shallow muddy 

 bottoms, the pebbles may have been taken with their food uninten- 

 tionally. I doubt this, however. I may add that all specimens do 

 not reveal similar pebbles. In the specimen of Boliekorhynchops 

 osborni, described in the preceding pages, where one would certainly 

 expect to find them, there were none. Possibly it was only the 

 broad-headed and more omnivorous kinds that resorted to this 

 peculiar diet, the long-snouted types being more exclusively fish-eat- 

 ing in habit. 



Crocodiles and seals are said to have similar habits, but I have 

 not learned the reason therefor. 



Many years ago, a similar habit was recorded of the teleosaurs 

 by Geoffroy St. Hilaire, in the Memoires de l'Acad. des Sci. , xxii, p. 

 48, 1833. Of the plesiosaurs, the only recorded notice, other than by 

 myself, that I can find of such habits is the following by Seeley 

 (Quart. Jour. Geol. Soc, xxxiii, 1877, p. 546): 



"In the lower dorsal region of the animal {Muraenosaurus gard- 

 neirt) about a peck of ovate and rounded pebbles occurred, varying in 

 size from a diameter of a quarter of an inch to a length of nearly two 

 inches. They are chiefly of opaque milky quartz, several are of 

 black, metamorphosed slate, and .a few of altered, fine-grained sand- 

 stone and ironstone, some of the pebbles showing a veined character, 

 such as might be derived from the neighboring Paleozoic rocks of the 

 north of France. Pebbles being of such rare occurrence in thcGault, 

 it would seem natural to account for these associated ones by the 



