No. 2.] COPE ON MIOCENE RODENTIA. 6 i 6 



A few bones accompany the mandible, all liaving been cut from the 

 same fragment of matrix. The head of the femur is perfectly round, 

 and is bounded by a well-defined neck. The great trochanter incloses 

 a large fossa. The lesser trochanter is large ; the third trochanter is 

 not prominent as it is in C. viciacensis. The shaft is generally flattened, 

 with its long diameter transverse. The condylar extremity is flattened, 

 and the rotular groove is wide, and the condyles well separated. The 

 cpicondylar angles are distinct, but not so prominent as in 8. viciacensis 

 (see Filhol, I. c, PI. VI, Figs. 13, 14). The general form of the femur 

 is robust, as in that species. 



The distal extremity of the tibia resembles that of Sciuridce generally, 

 especially in the large size of the external posterior angle. Its diameters 

 are small, and the distal part of the shaft is slender and subcylindrical. 

 The crest extends well down from the proximal end, being much stronger 

 than in the true squirrels, and bounds a longitudinal fossa. The fibular 

 facet of the tibia overhangs extensively, and bounds a rather narrow 

 proximal fossa. This continues into a narrow shallow groove on the 

 posterior face of the shaft, which disappears near the middle of its 

 length. The proximal half of the shaft is much compressed. The inner 

 fiice is smooth and gently convex. The crest sinks rapidly into the 

 head, and the femoral facets are well separated. The tibia resembles 

 that of G. viciacensis, but is more compressed in its proximal half. 



Measurements of Mad leg. 



ir. 



Lengtli of femiir 057 



Width offemnr atliead 019 



Width of femur shaft below third trochanter 009 



Width of femur at epicondyles 015 



Width of condyles of femur 013 



Antero-posterior diameter at condyles Oil 



Antero -posterior diameter of head 009 



Diameters of head of tibial ''^"^''^'^P^'^^"^'^ i!!! 



( transverse 014 



ibi n ^ anteroposterior OOdC 



I transverse 008i: 



above middle 010 



Diameters of distal end of tibia? anteroposterior OOdO 



c transverse vVso 



Antero posterior diameter . 



( below middle OUo 



I have referred to this species in former catalogues of the vertebrate 

 fauna of Oregon as the Castor nehrascensis of Leidy. It is very nearly 

 allied to that species, but I find the following differences : First, the 

 postorbital constriction is narrower; second, there are fewer fossettes 

 on the posterior half of the molar teeth, but one or two. Leidy figures 

 two or three in the species described by him. 



MYLAGAULUS Cope. 



Bulletin U. S. Geological Survey of the Territories, IV, p. Z^A. May 3, 1878. 



Inferior molars three, rootless ; the first much larger than the others. 

 Enamel inclosing the first molar not inflected ; but numerous fossettes 



