184 NEBRASKA GEOLOGICAL SURVEY 



main feature of this collection, and of this preliminary report. 

 These skulls were found on levels separated by 75 feet of sedi- 

 ment, apparently aqueous in origin. Just half way down the 

 canyon, at a point named Quarry No. 2, were found the skull, 

 mandible, ribs, tusk, and a cervical vertebra of a species of young 

 " Tetrabelodon," somewhat similar to Trilophodon productus. 

 Seventy-five feet higher than this at Quarry No. i, near the rim 

 of the canyon, was found a much larger, different mastodon, with 

 skull, tusks, mandible, ribs, and pelvis. We have named these, 

 respectively, Tetrabelodon willistoni, and Eubelodon morrilli. 



TETRABELODON WILLISTONI, sp. nOV. 



This species, consisting of a nearly perfect skull with mandible, 

 one cervical vertebra and numerous ribs, was found in Quarry No. 

 2, about 115 feet below the general level, 75 feet below, and 

 about 300 feet distant from Quarry No. i. This species is named 

 for Dr. S. W. Williston. The skull lacks parts of the zygoma, one 

 exoccipital, part of the other, and the basioccipital. The man- 

 dible is without blemish. The skull is narrow, and with inferior 

 dome. The occiput, though slightly convex, is noticeably flat, and 

 is furrowed but little along the median line. There is a well- 

 marked, though broad, occipital crest. This is very unlike the 

 occiput in Elephas, which is noticeably convex. The exoccipitals 

 and parietals of Elephas round gently and without crest. The pit 

 is so deep that it extends well to the inner cranial wall. The 

 posterior nares are very narrow, and long postero-anteriorly. The 

 anterior nares are widely expanded with thick borders. The basi- 

 cranial bones are deflected only about 10 degrees from the palatine 

 plane. 



During the growth of a proboscidean, the size of the brain from 

 youth to maturity does not change much. Furthermore, in the 

 case of the young of Elephas, the proportion of the cranium to 

 the brain is quite normal. But in the case of adults, the skulls 

 are abnormally inflated by air cells, and this greatly emphasizes the 

 disparity between the relatively small brain cavity and the im- 

 mense skull. Though not an adult, the air cells in the skull of 

 Tetrabelodon willistoni are small, and the inflation moderate. It 



