Professor Harlan on the Fossil Beaver. 



Species. 

 1 . Osteopera platycephala. 



Char, Essent. Head flat, ventricose at the sides ; snout obtuse ; eyes 

 widely separated. 



Dimensions of the cranium compared with that of the full grown 

 Canadian beaver : (the extremity of the snout of the Osteopera, together 

 with the upper incisors, have been destroyed.) 



New Genus. Castor fiber. 

 Total length of the skull, 

 Length of the frontal bone, 

 Breadth of do. 



Length of the parietal bone, 

 Breadth of do. - * 



Length of the zygomatic arch, 

 Breadth of do. 



Width across from one zygoma to the other 

 Breadth of the palate bones between the molars, 

 Length of the zygomatic fossa, 

 Breadth of do. 



Length of the lower jaw not including the incisors. 

 Breadth of the same including the molars, 

 From the top of the coronoid process to the base of 



the jaw, • - 1 2 2 4 



Description. Frontal bone nearly double the length and breadth of 

 that of the common beaver, flat and scabrous, forming on each side a 

 semilunar ridge, projecting into the orbits ; orbit of the eye small, and 

 nearly circular, which is due, principally, to the extraordinary develope- 

 nient of the zygomatic processes of the temporal and jugal bones, which 

 are produced downward and backward, so as to conceal the posterior half 

 of the lower jaw, together with the teeth, anteriorly arched, scabrous, and 

 ventricose ; the jugal portions being developed anteriorly and inferiorly, so 

 as to form on each side a bony antrum, or cavity, capable of containing in 

 all two or three ounces of fluid, and communicating with the mouth by 

 large oblong openings, immediately anterior to the molar teeth ; the cavity 

 projecting posteriorly into the orbit, with which it has no communication ; 

 anterior to the orbit, above the cavity, is a bony canal, capable of admit- 

 ting the little finger, somewhat analogous to the infra orbitar foramen ob- 

 served in the skull of the genus Cavia. 



The structure of the inferior jaw is equally remarkable, and adapted in 

 every respect to the peculiarities of the upper jaw ; the whole of the lower 

 jaw is more slender and narrower than that of the beaver. In order to 

 admit a free passage from the bony cavities into the mouth, the molar 

 teeth and alveolar processes of the lower jaw are elevated, and the latter 

 are separated from each other anteriorly, so as to leave a capacious open- 

 ing, of an oval form, from the sack into the mouth ; the coronoid process 

 very small, and not projecting so high as the condyloid ; the latter also 

 small, rounded above and compressed ; angles of the lower jaw rounded ; 

 the inferior incisors slender in proportion to those of the beaver, arched on 



