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 (Pl. 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. 
It, 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 Dolichorhynchops 
osbornt, 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 mm 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 |’Acad. des Sci., xxui, 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., xxxiul, 1877, p. 546): 
‘In the lower dorsal region of the animal (Muraenosaurus gara- 
ner?) 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 the Gault, 
it would seem natural to account for these associated ones by the 

