284 Thorpe — New Genus of Oligocene Hycenodontidce. 



the lower third molar shows a very small incipient exter- 

 nal bnttress on the anterior lobe, but it is not of the same 

 character as in N. horridus. 



Hycenodon montanus Douglass 1901. 



Both jaws of two individuals are referable to this spe- 

 cies. One pair of rami, Cat. No. 12767, Y. P. M., was col- 

 lected at White River, Nebraska, and the other pair, Cat. 

 No. 12768, Y. P. M., in Gerry's canyon, Gerry's ranch, 

 Colorado. The latter has nearly all the teeth present, 

 and shows the characters mentioned by Douglass as dif- 

 ferentiating 1 this species. The second incisor is as large 

 as the third. Its anterior part is wedged between the 

 posterior parts of Ij and I 3 , that is, it is not situated so 

 far posteriorly as in N. horridus and H. cruentus. The 

 premolars especially, and the molars to a less extent, are 

 relatively higher crowned than in the other species of this 

 genus. 



Hycenodon crucians Leidy 1853. 



Part of a left ramus with P 4 , M l7 and M 3 , Cat. No. 12770, 

 Y. P. M., collected at Gerry's ranch, Colorado, is referable 

 to this genus. 



Specimen No. 10076 Y. P. M., collected near Hermosa, 

 South Dakota, consists of a skull, jaws, many vertebrae, 

 and many parts of the appendicular skeleton. These 

 bones do not show any marked deviations from the 

 description, given by Scott in 1894, of the osteology of 

 this genus. 



Hycenodon leptocephalus Scott 1887. 



A well preserved skull with jaws, together with an atlas 

 and one lateral metatarsal, Cat. No. 10075, Y. P. M., are 

 referred to this species, as the skull exhibits the long nar- 

 row cranium and the sutural union between the pterygoid 

 processes of the alisphenoid bone. Measurements of the 

 type of this species are lacking, and for these we must 

 derive our information from the statement that "in size 

 it slightly exceeds the H. crucians of Leidy" (Scott 

 1887, p. 152). 



Nearly all sutures in the Yale specimen are plainly visi- 

 ble, including the diagnostic character of the union of the 



