414 



University of California. 



[Vol. 3. 



the middle, supporting a median tubercle for muscular attach- 

 ment. The tubercle unites infei'iorly with a sharp median keel 

 which becomes less prominent toward the superior border of the 

 foramen magnum. Lateral ridges extend from the median tuber- 

 cle outward and downward over the mastoid as in the sheep. 



The base of the skull resembles that of Haplocerus, and the 

 foramina for the exit of the cranial nerves are the same in char- 

 acter and position as in that genus. The bullae are imperfectly 

 preserved in the type, but in another specimen (No. M8464) from 

 the Potter Creek Cave they are seen to be quite different from 

 the corresponding parts in existing North American cavicorns. 

 Instead of being high and narrow as in the cattle and sheep, they 

 are flattened, presenting interiorly a slightly concave surface with 

 diamond-shaped outline. Anteriorly and externally, the bound- 

 aries of this surface are sharply defined; posteriorly and inter- 

 nally they are less clear. The bullae are low, extending but a 

 short distance (6 mm.) below the level of the post-glenoid pro- 

 cess. In Ombos, the rugged bullae present a mammilated crest 

 interiorly, quite different from the flattened surface in Eucera- 

 tli< j rhi in . 



The free borders of the palatines at the anterior margin of 

 the posterior nares are pinched in a short distance below the 

 narial border, producing on either side a shallow fossa which is 

 not found in any of the North American cavicorns with which 

 this genus has been compared. 



The contour of the dental series is the same as in Ovis and 

 Haplocerus, and as in these forms the posterior palatine foramina 

 open on the maxillo-palatine suture. 



In the lateral aspect of the cranium (PI. 50) the superior 

 border of the temporal fossa is seen to be sharply limited by a 

 ridge which extends from the upper margin of the postorbital 

 bar beneath the base of the horn-core to the lateral border of the 

 occiput which bounds the fossa posteriorly. 



The malar arch is robust. That portion of it which is 

 included between the inferior orbital rim and the ridge which 

 extends backward as the lower border of the jugal process is 

 broader than in the domestic cattle. 



The lachrymal pit is a broad shallow concavity, limited above 



