430 SMITHSONIAN MISCELLANEOUS COLLECTIONS [vOL. 45 



of the tooth has two reentrant angles on its anterior face, and one 

 each on its internal and external faces. The second, third, and 

 fourth lower molariform teeth have their posterior portions as well 

 developed as their anterior portions, and the posterior limb of the 

 reentrant angle which divides these teeth into two portions is very 

 much more convoluted than in any of the other Leporidse examined. 

 The last lower molar has the appearance of a double cylinder, the 

 anterior portion of which is larger and elliptic in outline, and the 

 posterior portion smaller and more terete. 



Upper Extremity. — The bones of the upper extremity, like those 

 of the lower, are relatively shorter and stouter than in the other 

 genera. The double trochlear surface of the humerus has its main 

 portion very broad and shallow, while the outer portion is much 

 reduced in size. The groove subtending the internal condyle is very 

 shallow. 



The radius and ulna (pi. xcviii, lo) are short, heavy bones, the 

 ulna being the larger of the two. The radius is distinctly shorter 

 than the humerus. 



The carpal bones resemble those of the Leporidse as described in 

 the general account (page 378), but the pisiform is considerably re- 

 duced in size, and has almost the same form that it has in Ochotona. 



The metacarpals are short and heavy, resembling those of Ocho- 

 tona, and the basal width of the three middle ones is contained but 

 one and a half times in the length of the middle metacarpal. 



Lozvc)' Extremity. — The femur is very stout and heavy. 



The tibia and fibula are also very stout and heavy, in marked con- 

 trast to the same bones in the other genera. As in the case of 

 Romcrolagus the fibula fuses with the tibia at its middle point (pi. 

 xcix, 4). 



The hind foot (pi. c, 4) is short and stout, the tarsal bones being 

 relatively wider than in the other genera of the Leporidse, having 

 about the same general proportion as in the Ochotonidse. 



The metatarsals are especially short and heavy, and their basal 

 width is contained but one and a half times in the length of the 

 longest, as in the case of the Ochotonidse. 



Pentalagiis is the most marked of any of the genera of the 

 Leporidse, the tooth formula, the structure of the teeth, the relative 

 size of the radius and ulna, and the very short tarsus and metatarsus 

 being peculiar to the genus and unlike anything in the rest of 

 the family. A complete skeleton would probably show that it has 

 still further points of differentiation from the typical leporine form. 



