LAGOMORPHA. 881 



alveolar ridge is not distinguishable from the inferior border in L. sylvaticus. 

 In the same species there is but one, the usual mental foramen, in the posi- 

 tion of the anterior one of the extinct species. The spongy condition of 

 the rami near the symphysis in the L. sylvaticus is not seen in the extinct 

 species. Excepting the first tooth, the inferior molars are of similar size 

 and constitution in the two species. 



It is probable that the Lepus ennisianus, described a few pages later in 

 the present work, is the intermediate form in the line of descent between 

 the Palceologus haydeni and the Lepus sylvaticus, or perhaps the L. aiiduboni. 

 This species is from the John Day Miocene of Oregon, a later deposit than 

 the true White River. The last inferior molar is like that of the P. haydeni, 

 while the first molar is that of the genus Lepus. The postorbital process, 

 though present, is smaller than in any existing Noith American species. 



The Palceologus haydeni was excessively abundant during the White 

 River epoch in Dakota and Colorado, as the number of its remains indicate. 

 I find, also, quite a number of maxillary and mandibular bones with teeth, in 

 my Oregon collections, which I cannot distinguish from the present species. 

 I have made the identification provisionally, in anticipation of the discovery 

 of more perfect material. 



Pal^olagus triplex Cope. 



Paleontological Bulletin No. 16, p. 4. Annual Report IT. S. Geol. Surv. Terrs., 1873 (1874), p. 479. 



Plate LXVI; fig. 28. 



This rabbit is known from a single incomplete left mandibular ramus, 

 which supports all the molar teeth in perfect preservation. It belonged to 

 an adult animal, but the first inferior molar is but little worn, showing that 

 the individual had but just attained maturity. 



This species is larger than the Palceolagus haydeni, and is equal in size to 

 the P. turgidus. It difi'ers materially from both species in the constitution 

 of its molar teeth. The first molar is peculiar in having an anterior as well 

 as an external groove, the result being a trilobate instead of a bilobate sec- 

 tion. This character would be maintained during the life of the animal, as 

 the groove continues well into the alveolus. The four intermediate molars 

 are characterized by the presence of a third column posterior to the second, 

 and of smaller diameter. It is at first isolated from the second by enamel 

 56 c 



