copc.j -'-^" [July II!. 



The extremity of the femur is remarkably broad and depressed ; it ex- 

 pands a little at the condyles. The trochlear groove is but little raised 

 above the plane of the anterior (superior) face of the femur, vi'hile its lat- 

 eral bounding ridges are strong, the inner the more prominent. The 

 width of the groove is about equal to the transverse diameter of the 

 tuberosity on the inner side, and greater than that of the outer. The 

 faces of the condyles are quite inferior, and sub-depressed, the outer ex- 

 tending rather more posteriorly than the inner. Both are so separate 

 from the trochlear groove as not to have had any continuous face with it; 

 this is not entirely clear, as the surface is slightly injured at the point of 

 connection. The inter-condyloid fossa is continuous both with the infe- 

 rior face of the femur, and with the trochlear groove, without separating 

 ridges, as many rodents exhibit. Just above the inner condyle there is 

 a strongly marked fossa of a regularly rounded form. 



The general character of the two femora confirms those of the teeth, as 

 of a large rodent. The form and relations of the articular faces difl'er 

 alike from those exhibited by Carnivores, Ungulates and Edentates. The 

 patella, which pertains to one of the femora, is an elongate bone, with 

 thinned and rounded distal extremity. The proximal portion is lost, but 

 at the fracture the section is very convex. More distally it is flat. 



]n. Liii- 



Width femur just above condyles 2 3.7 



Depth " " " 14. 



Width at tuberosities 3 4.8 



" trochlear groove, distally IG. 



" inner condyle 14.2 



' ' outer • ■ 18. 



" intercondyloid fossa 7. 



Length fragment patella 3 6. 



Width at middle " 14 G 



Depth at fracture 10.4 



LoxoMYLUS, Cope. 



Molars straight, prismatic, composed of three dentinal columns, one of 

 which is incurved, but none closed at the base. The triturating surface 

 very oblique in the vertical direction, indicating the greater elevation of 

 the teeth at one extremity of the series than the other. A horizontal 

 obliquity of the dentinal columns is produced by their lateral displace- 

 ment. Enamel places but slightly curved. An external cementum layer. 



This genus differs in many points from Amblyrhiza ; these are, the lack 

 of one and two dentinal columns ; the double obliquity of the crowns, the 

 absence of curvature, and less closure of the base. It is nearer to Arch- 

 aeomys Laiz. et Par., but differs in two points ; that the upper molars 

 have but three dentinal columns like the lower, instead of four, and that 

 the horizontal grinding surface is oblique. This last peculiaVity alone 

 seems to distinguish it from Lagidium and Chinchilla, indicating a rela- 

 tion to the latter similar to that between the great extinct beaver of 

 Europe Trogontherium c u v i e r i , aiid the existing genus Ca.stor. 



