CASTOIUDiE— STENEOFIBEE— S. NEBEASCENSIS. 451 



ingly well-marked differences will be found in other features of the skull 

 when we are able to study this interesting form from more nearly perfect 

 specimens. 



The following table, showing the comparative measurements of Eucastor 

 tortus with the corresponding portion of the skull of Castor fiber, is from Dr. 

 Lcidy's memoir on the " Extinct Mammalia of Dakota and Nebraska'' (Jo urn. 

 Acad. Nat. Sci. Phila., 2d ser., vol. v, p. 342). 



C. tortus. C. fiber. 

 Lines. Lines. 



Length of space occupied by four molars G£ 13 



Length of hiatus from first molar to incisors 12 J 21 



Breadth of face opposite first molars 7 14 



Breadth of face in advance of infra-orbital foramen 5} 11 



Width of palate between first molars 1 3i 



Width of palate between last molar alveoli 4 7 



Antero-posterior diameter of first molar 2 3 



Transverse diameter of first molar 2£ 3J 



Antero-posterior diameter of second molar 1J 8 



Transverse diameter of second molar 2 3 J 



Antero-posterior diameter of third molar 1$ 3 



Transverse diameter of third molar 2 34; 



Diameter of incisors 2 3i 



Genus STENEOFIBER E. Geoffr. 



" Stencofiber E. Geoffroy, Revue Eneyclop., 1833, — ." 



Palwocastor Leidy, Journ. Acad. Nat. Sci. Phila., 2d ser., v, 1'869, 338. 



STENEOFIBER NEBRASCENSIS Leidy. 



Stcneofiber nebrascensis Leidy, Proc. Acad. Nat. Sci. Phila., 1856, 80; 1857, 89. 

 ChaUcomys nebrascensis Leidy, Proc. Acad. Nat. Sci. Phila., 1857, 176. 



Paleeocastor nebrascensis Leidy, Journ. Acad. Nat. Sci. Phila.,2d ser., v, 1869, 338, 405, pi. xxvi, figs. 7-11 ; 

 U. S. Geol. Survey of Wyoming, 1871, 363. 



The present species was first described by Dr. Leidy, in 1856, from 

 specimens collected by Dr. Hayden from the Mauvaises Torres of the White 

 River, Dakota. These specimens indicate an animal of about the size of 

 Eucastor tortus. The species is thus far known from "a much mutilated skull, 

 with the fragments retained nearly in their original position by a mass of 

 included calcareous matrix. The greater part of the cranium is destroyed, 

 as is also the nose and parts of the jaws, though all the teeth are preserved. 

 A second specimen consists of portions of both jaws of an aged individual, 

 badly mutilated and imbedded in a mass of matrix. The remaining speci- 

 mens, from a third individual, consist of portions of both sides of the lower 

 jaw and one side of the upper jaw, containing all the molar teeth, and freed 

 from investing matrix." 



