120 PROCEEDINGS OF THE NATIONAL MUSEUM vol. <SR 



jaw and the lower part of the lingual surface turn outward just 

 anterior to P., somewhat more sharply than in Hypoloxius veins. 

 Compared with specimens of Lepus townsendii having a P3 of about 

 the same size, the anterior portion of the Alilepus? vagus jaw is much 

 shorter, deeper anteriorly, and exhibits the base of a distinctly 

 broader incisor. 



Presumably, the most distinctive feature is the enamel pattern of 

 P3, which exhibits in addition to the two external reentrant folds seen 

 in Eypolagus a deep internal fold extending nearly to the posterior 

 external fold. The heavy enamel of the anterior portion of the inter- 

 nal fold forms with the anterior portion of the posterior external fold 

 a prominent, but discontinuous, transverse ridge on the occlusal 

 surface. The posterior external fold extends about halfway across 

 the tooth and near its inner extremity shows a slight flexure. The 

 anterior external reentrant fold is moderately shallow and rounded 

 internally. The anterior column of P3 is more nearly triangular in 

 cross section than this portion of P3 in the Hagerman Hypolagus 

 material. 



Alilepusf vagus^ as indicated by the enamel pattern of P3, appears 

 to be related to the species Lepus OMnectens Schlosser, which Dice ^^ 

 has made the type of Alilepus, from the Upper Miocene or Pliocene 

 of northern China and Mongolia. The Idaho form is somewhat 

 smaller, judged by the measurements given by Schlosser and by 

 Young,^^ and the antero-external angle of P ^ is sharper and more 

 outstanding. In the figure given by Young for the specimen from 

 northern China the external reentrant folds in P3 appear much less 

 deeply impressed than in the Idaho specimen. 



The small rabbit Romerolagus diazi, now living on some high 

 mountain peaks in Mexico, exhibits an internal reentrant fold on P3. 

 In this type the internal fold is much constricted or closed at the 

 lingual surface of the tooth, and the posterior portion of the fold is 

 finely crenulated, as are the anterior surfaces of the posterior col- 

 umns of P4 to M2, inclusive. 



It is possible that Alilepusf vagus was derived from the Asiatic 

 group. A wide distribution for this genus would not be unexpected 

 considering the presence in the living fauna of North America of the 

 unique Bo7ne7'olagus, the relations of which may be closer to such 

 forms as Alilepus than to Lepus and SylvUagus. However, whether 

 phylogenetic speculations are warranted by the implications of the 

 pattern of P3 remains to be demonstrated. 



"Dice, L. R., Journ. Mamm., vol. 12, no. 2, p. 159, 1931. 



1^ Young, C. C, Pal. Sinica, ser. C, vol. 5, fasc. 3. pp. G2-63, pi. 3, flgs. 12, 13. 1927. 



