No. 2.J COPE ON MIOCENE KODENTIA. 381 



crown descends to its base, and hence persists longer than in the typi- 

 cal JEntoptycM. 



I am acquainted with two species of this genus. The posterior part 

 of the skull of an individual represents a third species, which I refer 

 provisionally to this genus. 



The characters of the species are as follows : 



I. Otic and mastoid bullse continuous. 



Temporal ridges uniting into a sagittal crest ; length, of skull .043 ; supraor- 

 bital ridges and concave front P. sulcifrons. 



Temporal ridges not uniting ; length of skiill .035 ; interorbital region flat ; no 

 ridges P. leptophrijs. 



II. Otic and mastoid bullae separated by a deep groove. 



Temporal . ridges not united ; front concave ; size medium ; supraoccipital 

 wide P. diplophysus. 



LAGOMORPHA. 



PALAEOLAGUS Leidy. 



Proceedings Academy Philada. 1856, p. 89 ; Extinct Mamm. Dakota and Nebraska, 

 p. 331.— Cope, Ann. Eeport U. S. Geol. Survey Terrs. 1873 (1874), p. 477. 



Family Leporidce. Dentition: I. f ; 0. ^; M. f j or, Pm. f, M. f. 

 Superior incisors sulcate, inferior incisors not sulcate. First and last 

 superior molars simple, intermediate ones with an enamel inflection of 

 the inner side, which soon wears out. First inferior molar of one more 

 or less transversely divided column ; other inferioi* molars consisting of 

 two columns in antero-posterior relation. ISTo postfrontal process. 



The above characters approximate nearly those of the existing genus 

 Lepus. The only distinction between them i<ignalized by Dr. Leidy, is 

 the more simple first inferior molar of the extinct genus, which consists 

 of one column more or less divided. In Lepus this tooth consists of 

 two columns, the anterior of which is grooved again on the external 

 side in the known species. I am able to reinforce this distinction by a 

 strong character, viz, the absence of the postfrontal process in Fake- 

 olagiis. As compared with the extinct genus Titanomys of Meyer,* 

 the difference is well marked, as that genus has the molar teeth f instead 

 of f . The last inferior molar is cylindric, consisting of but one column. 

 The first inferior molar consists of two cylinders broadly united, as in 

 the corresponding tooth of Palaeolagus. As compared with Panolax 

 Cope,t which is only known from superior molar teeth, this genus may 

 be at once recognized by the simplicity of the last tooth. In Panolax it 

 consists of two columns. 



Dr. Leidy's descriptions and figures, which are available for the defi- 

 nition of this genus, relate exclusively to the dentition. Characters 



* Amplulagus. Catal. M6th. et Descr. Vert^bres Fossiles de la Bassiu de la Loire, 

 1853, p. 42. 

 t Eeport Lieut. G. M. Wheeler, 4 to, IV, p. 296. 



