1917] 



Dice: American Tertiary Lagomorphs 



181 



The posterior part of the jaw is very different in shape from that 

 of any living lagomorph. The region for the attachment of the mass- 

 seter muscle is very weakly developed, and, as stated by Cope,' the 

 masseteric fossa is entirely posterior to the tooth row. 



(m 



Fig. 2 Fig. 3 



Fig. 2. Archaeolagus ennisianus (Cope). Left lower molariform teeth (except 

 M 5 ), X 3. Univ. Calif. Coll. Vert, Palae. no. 1267, X 3. John Day beds, Oregon. 



Fig. 3. Archaeolagus ennisianus (Cope). Eight M, and M 5 , X 3. Univ. Calif. 

 Coll. Vert. Palae. no. 339, X 3. John Day beds, Oregon. 



The skull indicates that the John Day animal had approximately 

 the size of Sylvilagus floridanus. However, the skull is more slender, 

 and the braincase has a much smaller capacity than that of any Recent 

 rabbit. 



HYPOLAGUS,"' new genus 



Type species Lepus veins Kellogg' 5 



One jaw is known from the Middle Miocene, Virgin Valley beds. 

 Two jaws, one of them the type specimen, and one upper molar are 

 known from the Pliocene, Thousand Creek beds. Both localities are 

 in Humboldt County, Nevada, 



In this genus P3 has two exterior re-entrant angles, neither of 

 which extends over half way across the tooth. The posterior angle is 

 much deeper than the anterior. There are no grooves on the inner 

 surface of the tooth. The upper molar has the re-entrant angle ex- 



Fig. 4 Fig. ■) 



Fig. 4. Hypolagus vetus (Kellogg). Left lower molariform teeth, X 3. Univ. 

 Calif. Coll. Vert. Palae. no. 12567. Thousand Creek beds, Nevada, 



Fig. 5. Hypolagus vetus (Kellogg). Upper molariform tooth, X 3. Univ. 

 Calif. Coll. Vert. Palae. no. 21868. Thousand Creek beds, Nevada. 



tending about half way across the crown and the enamel in the angle 

 is coarsely folded. Cement is well developed on the teeth, particularly 

 on the specimens from Thousand Creek. 



< Cope, E. D., Bull. U. S. Geol. Surv. Terr., vol. 6, p. 385 (1882). 

 •"• 0tt6, under; \ayu>s, hare. 



« Kellogg, L., Univ. Calif. Publ. Bull. Dept. Geol., vol. 5, p. 436, fig. 20 (1910). 



