280 Thorpe — New Genus of Oligocene Hycenodontidce. 



rami. The posterior position of I 2 is typical of the 

 creodont carnivorous type. It is quite probable that this 

 skull and jaws belonged to a male. 



Measurements of Dentition. 

 (Cat. No. 10074, Y. P. M.) 



mm. 



Superior molar-premolar series, length . . . 137 



Superior molar series, length 50.5 



Inferior molar-premolar series, length 141 



Inferior molar series, length 66 



A single right M 3 , in part of the jaw No. 12765, Y. P. M., 

 from White River, Nebraska, indicates an individual 

 approximately as large as the one described last above. 

 It measures 35 mm. fore and aft, with a maximum trans- 

 verse diameter of 13.5 mm. 



The cotype, No. 12766, Y. P. M., shows very clearly the 

 cranial foramina. The auditory bullae are lacking and 

 I am not sure whether or not any were ever present. If 

 this genus did have them, they were circular in basal out- 

 line, with a diameter of approximately 18.5 mm. The 

 maxillo-palatine suture is obtuse at its anterior margin, 

 which lies opposite the middle of P 4 ; the postorbital con- 

 striction is at the coronal suture; the posterior nasal 

 bones are acute, extending nearly to a line through the 

 middle of the orbits ; the lacrymal is relatively small, 

 extending somewhat in front of and below the orbit, and 

 bears a slight depression, which appears greater than it 

 actually is due to the elevation of the orbital margin on 

 which is a prominent lacrymal tubercle ; the infra-orbital 

 is quite large ; and the hamular process is represented by 

 a distinct rugosity, approaching very close to a tubercle 

 in character. 



Comparison with Hymnodon. — Neohycenodon differs 

 from Hycenodon in several distinct ways, among others in 

 the development of an external buttress-like ridge on the 

 paraconid of the last lower molar, but the most important 

 difference lies in the structure of the basicranial and con- 

 tiguous regions. The superior part of the glenoid articu- 

 lar surface is more than 15 mm. below the basioccipital, 

 and in part lies below the bulla, while the postglenoid 

 tubercles are on a line only 14 mm. anterior to the basion. 



