PLIOCENE HARES FROM IDAHO — GAZIN 117 



limnetus, and the condyle is considerably lower and somewhat more 

 posterior in position. The first cheek tooth of H. hroumi is rather 

 distinctive and apparently shows some variation in the enamel 

 pattern between specimens. In three lower jaAvs tlie posterior ex- 

 ternal fold in P3 extends slightly more than halfway across the tooth 

 and near its inner extremity shows one to three plications. A fourth 

 specimen, that figured by Dice, shows an enamel lake near the lingual 

 side of P3, opposite the posterior external fold. 



There is in the Anita collection a jaw portion exhibiting all cheek 

 teeth except M3, a specimen not examined hy Hay or by Dice since 

 the matrix has only just been removed. The jaw corresponds closely 

 in size with those recognized as Hyfolagus trowni^ but P3 is a little 

 larger and the posterior reentrant fold extends completely across 

 the tooth and is open internally. A short distance below the oc- 

 clusal surface, however, this fold is cut off internally. Also, there 

 is present a slight groove on the anterior surface. This specimen 

 may represent a species of SylvUagus or Lepus^ or possibly represent 

 an extreme variant of H. hrownl in which the teeth are perhaps at an 

 earlier stage of wear than in other specimens. 



The lepores from the Miocene are in general of a more primitive 

 type than the Thousand Creek Hypolagus vetus and show a closer 

 approximation to the conditions seen in the John Day Archaeolagus 

 ennisianus. Species in this category include Archaeolagus? macro- 

 cephalus (Matthew )° and Archaeolagus? primigenius (Matthew) 

 from the Upper Rosebud of South Dakota and Hypolagus? apachen- 

 sis Gazin *^ from the Upper jMiocene of southern California. Illus- 

 trations and measurements for the types from the Rosebud were 

 given by E. R. Hall '^ incidental to a descriptioii of the rabbit ma- 

 terial from the later Tertiary at Fish Valley, Nev. 



Remarks. — The skull of Hypolagus limnetus is decidedly modern 

 in appearance but has retained to a certain degree many of the 

 primitive characters observed in Palaeolagus. Several of those 

 characters in which the Hagerman form differs from modern Sylvi- 

 lagus and Lepus are suggestive of conditions more conspicuous in 

 the Oligocene rabbits. These include the shorter rostrum; less de- 

 pressed cranium, which is associated with a smaller angle between 

 the basifacial and basicranial axes; large, less widely separated 

 bullae; anteroposteriorly elongate basioccipital; a more constricted 

 posterior nasal passage; deeper zygomatic arches; and presumably 

 simpler postorbital jDrocesses. The dentition of H. limnetus is quite 

 removed from that in Palaeolagus but may well have been derived 

 from the latter through such forms as Archaeolagus ennisianus. 



"Matthew, W. D., Bull. Amer. Mus. Nat. Hist., vol. 23, pp. 214-216. 1907; vol. 50. 

 pp. 86-87, 1924. 



"Gazin, C. L., Carnegie Inst. Washington Publ. 404, pp. 67-69, pi. 3. figs. 1-4, 1930. 



7 Hall. E. R., Univ. California Publ. Bull. Dept. Geol., vol. 19, pp. 308-311. figs. 25-28, 

 1930. 



