POSITION IN ANIMAL KINGDOM. 39 



ver has likewise been found in a fossil state. On this 

 subject, Baird remarks: "The bone caves at Carlisle 

 yielded a large number of remains of beaver, both 

 young and old. There are no satisfactory points of 

 dijBference from the existing species, although in size 

 some of the teeth are larger than any recent speci- 

 mens I have seen, indicating a length of quite six 

 inches for the skull. "^ 



As the European beaver has its prototype in the 

 Trogontlierium, so the American species had its fore- 

 runner in Castoroides, a gigantic fossil beaver, surpass- 

 ing in size all existing as well as extinct rodents. 

 But few specimens have as yet been found. The first 

 was described by Foster and named Castoroides Ohio- 

 ensis; and the second by Hall and Wyman. The lat- 

 ter was found in a lacustrine formation subsequent to 

 the drift in Wayne County, New York. From the 

 geological relations in which these fossil remains were 

 discovered. Hall pronounces Gastoroides cotempora- 

 neous with the mastodon. The skull, measured from a 

 cast in my collection, is ten inches and fifteen hun- 

 dredths in its greatest length, and seven inches and 

 sixty hundredths in its greatest width. He must 

 have been five or six times larger than the beaver of 

 the present time. Baird observes that the genus Cas- 

 toroides is nearer to the genus Trogontlierium than to 

 Castor, which is an interesting fact, showing that the 

 fossil genera are nearer to each other than either is to 

 the existing genus. 



Although it thus appears that three distinct genera 

 of the beaver family — if Trogontlierium stands inde- 



* Explorations for a Railroad Route, etc. to the Pacific, viii. 361. 



