Apr. 1903. NortTH AMERICAN PLESIOSAURS—WILLISTON. 75, 
A PECULIAR FOOD HABIT OF THE PLESIOSAURS. 

More than twenty years ago, Professor B. F. Mudge published, 
in the First.Biennial Report of the Kansas State Board of Agricul- 
ture (p. 62), the following: ‘‘In the Plesiosaurs we found another 
interesting feature showing an aid to digestion, similar to that of many 
living reptiles and some birds. This consisted of well-worn siliceous 
pebbles, from one-fourth to one-half an inch indiameter. They were 
the more curious, as we never found such pebbles in the chalk or 
shales of the Niobrara.’”’ The specimens which led to this conclusion 
were collected while I was a member of Professor Mudge’s party, and 
are now preserved in the Yale collection. Nearly ten years ago some 
plesiosaur bones collected near Ellsworth, Kansas, from the Benton 
limestone, were sent to the Kansas University museum, together with 
a lot of siliceous stones, with a request for information concerning 
both. At the first opportunity I visited the locality whence they had 
been discovered and collected what had been left of the specimen. 
The bones were in a poor state of preservation, due to the effects of 
frost, but by carefully digging over the shale in which they occurred 
we obtained about one hundred and twenty-five of the pebbles, 
together with several dorsal vertebra and ribs. Some of the pebbles 
were still attached to the ribs by the original matrix, making it cer- 
tain that their deposition was contemporaneous with that of the skel- 
eton. The plesiosaur is one of the largest of the order, the dorsal 
centra measuring five or more inches in diameter. In all probability 
the species is identical with that mentioned in the preceding pages 
as coming from the vicinity of Beloit. It is impossible to 
determine the: genus, and the species is yet undescribed. The 
pebbles vary in weight from less than one gramme to more 
than one hundred and seventy grammes. The smaller ones were 
worn into more or less perfect ellipsoids, but the larger ones are 
more irregular in shape, having suffered less abrasion. It seems 
probable that the most of the pebbles had been obtained by the 
animal from the sea beaches bordering the Black Hills, but not a 
few of them, consisting of red quartzite, are quite identical with the 
quartzite boulders so often found in the drift of eastern Kansas, 
which have come from the vicinity of Sioux City, Iowa. 
The specimens show conclusively that the pyloric orifice of the 
plesiosaurs must have been well provided with a sphincter, and that 
no solid substances passed into the intestinal canal. One need 
