116 PROCEEDINGS OF THE NATIONAL MUSEUM vol. S3 



and P3 is a little shorter and the anterior surface of the ascending 

 ramus rises more steeply, placing the condyle slightly higher and 

 a little farther forward than in the living rabbit. 



As is true in the upper dentition, the size of the lower teeth can be 

 closely matched in specimens of Sylvllagus nuftdlli grangeri. The 

 lower incisor shows a longer bevel, apparently accompanied by a 

 slightly more acute cutting edge; also the posterior surface of the 

 incisor does not show the slight longitudinal concavity or groove 

 commonl}^ present in S. nuUalli grangeri. P3 (fig. 3&) shows the 

 pattern ty]^ical of Hypolagus in which the posterior of the two 

 external reentrant folds extends only about halfway across the tooth, 

 there being no reentrant from the internal surface. The anterior 

 external fold, however, appears more deeply impressed than is usual 

 in Hypolagus. In SylviJagiis and Lepiis the posterior external re- 

 entrant fold extends nearly or entirely to the internal surface of 

 the tooth, and the anterior surface of the anterior column is com- 

 monly complicated by one or more shallow reentrant folds or grooves. 

 The molariform lower cheek teeth of the fossil show no important 

 characters distinguishing tliem from these teeth in the sage cottontail 

 of Idaho. 



Comparison. — Hypolagus Jimmetus is distinctly smaller and less 

 robust than Hypolagus vet/us., or the large Hagerman form close to 

 H. vet us. The lower jaw is slenderer, shallower, and has teeth 

 about one-fourth smaller. The two enamel folds on the anterior 

 surface of P- are much shallower at the stage of wear observed than 

 in H. vetus, whereas the lingual reentrant folds on the upper molari- 

 form teeth appear somewhat more deeply impressed; also the an- 

 terior external fold on P3 appears to be deeper than in //. vetus. 



Hypolagus edensis Frick,^ from the Eden Pliocene beds in south- 

 ern California, is apparently somewhat smaller than H. limnetus. 

 The anterior external enamel fold of P3 in H. edensis appears rather 

 deep, but is placed more nearly on the anterior surface of the tooth. 

 Also, the figures of the lower molariform teeth show them to be 

 more rounded internally than in 77. Um.netus. 



HypoJagus hrowni (Hay)* from the early Pleistocene occurrence 

 at Anita, Coconino County, Ariz., is a small species, intermediate 

 in size between Hypolagus limnetus and Brachylagus idahoensis. 

 The anterior portion of a skull, U.S.N.M. no. 10197, of H. hrowni 

 shows few differences other than that of size from the skull of H. 

 limnetus. The u]:)per molariform teeth in the two species are similar, 

 although the median fold in each of the teeth appears somewhat more 

 crenulated in H. liinnetus. The lower jaw of H. hrowni is distinc- 

 tive in that the ascending ramus rises much less steeply than in H. 



'Frifk, Childs, Univ. California Piibl. Bull. Dept. Geol., vol. 12, p. 348, figs. 52, 53, 1921. 

 * Hay, O. P., op. cit., pp. 630, 631, 1921 ; also Dice L. R., op. dt., 1932. 



