182 University of California Publications in Geology [Vol.10 



The posterior re-entrant angle of P 5 in the Virgin Valley specimen 

 is somewhat different from that in the type specimen, and the shape 

 of P3 differs in the two. There are also some differences in the com- 

 parative size of various other teeth. It may be that the Virgin Valley 

 form should be placed in a separate species, but the amount of material 

 now at hand is too scanty to permit a satisfactory determination of 

 this point. 



P3 in Hypolagus differs from the corresponding tooth in Archae- 

 olagus in being proportionally shorter and broader, although the 

 enamel pattern is very similar in the two genera. Hypolagus further 

 differs from Archaeolagus in having the re-entrant angles of the 

 molars coarsely folded, whereas they are simple in the John Day 

 species. Also, in Hypolagus the region of the jaw for the attachment 

 of the masseter muscle is well developed, as in modern rabbits, and is 

 not weak, as in Archaeolagus. 



In the characters of the teeth and skeleton Hypolagus is in general 

 more simple than Lepus, and may be considered a form near the 

 probable ancestor of that genus as well as of several other modern 

 genera. Archaeolagus is a form much more primitive than Hypolagus, 

 and might well have been its progenitor. 



A single specimen, consisting of part of a lower jaw and the teeth, 

 except M3, is known from the Middle Miocene, Virgin Valley beds of 

 Humboldt County, Nevada. 



Fig. 6. Oreolagus nevadensis (Kellogg). Lower molariform teeth (except M,), 

 X 3. Univ. Calif. Coll. Vert. Palae. no. 12575. Virgin Valley beds, Nevada. 



The form is evidently a lagomorph, as the lower molar teeth are 

 formed of two columns, one posterior to the other. The species, how- 

 ever, seems to have closer affinities to the Ochotonidae than to the 

 Leporidae, for the posterior column of the molariform teeth is at- 

 tached to the anterior column in a narrow neck, rather than by a 

 broad union extending nearly across the tooth, as in the Leporidae. 



7 cipos, mountain ; \ayu>s, hare. 



s Kellogg, L., Univ. Calif. Publ. Bull. Dept. Geo!., vol. 5, p. 485, figs. 19a and 

 196 (1910). 



OREOLAGUS,? new genus 

 Type species Palaeolagus nevadensis Kellogg' 



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