502 Bulletin American Museum of Natural History. [Vol. XV I, 



collections. The former is an older animal than Leidy's 

 type, the latter younger. The species appears to be dis- 

 tinguishable by the long, narrow muzzle, small bullae, sharp 

 sagittal crest, and small brain-case. The postorbital constric- 

 tion is moderate, the pattern of the teeth rather complicated, 

 two deep fossettes anterior to the external inflection on p* 

 remaining in the well-worn teeth of No. 1428. 



2. S. peninsulatus. Besides the type skull, another skull, 

 less crushed, a skull and jaws, and several parts of jaws, etc., 



referable to this species, are 

 in the Cope Collection in this 

 museum. It is a more robust 

 species than the last, distin- 

 guishable by the large bullae 

 and probably by the broader 

 muzzle, wide occiput, larger 

 brain-case, and wider sagittal 

 crest. The postorbital con- 

 striction is very narrow in the 

 type, but not in the second 

 specimen. The teeth are 

 much like those of 5. nebrascensis, but the second anterior 

 fossette of p* apparently remains longer as a branch from 

 the medial external enamel inflection. The fossette remaining 

 from the posterior external enamel inflection of p* has almost 

 disappeared in the type and another specimen, but shows no 

 signs of breaking up into three little fossettes, as it apparently 

 has done in the type of 5. nebrascensis. The specific validity 

 of these distinctions in the tooth pattern is very ques- 

 tionable; the two sides of a single skull seldom agree at 

 all closely, and this may well be an advanced mutation or 

 subspecies of 5. nebrascensis, the large bullae being the 

 clearest distinction. 



3. S. gradatus. The type skull, and the palate of a some- 

 what older individual are in the Cope Collection. It is a 

 smaller animal than the two preceding species, with short, 

 wide muzzle, postorbital constriction moderate, brain-case 

 short and rounded, temporal crests not uniting to form a single 



Upper 



Fig. 6. Steneofiber petiinsztlatiis. 

 and lower molars, x |. Type. No 

 John Day (? Diceratheriura Beds), Oregon 



