304 IF. B. Scott — Some New Forms of the Dinocerata. 



and bruin, and assumes that the two groups had a common 

 ancestor, if indeed the one did not stand in an ancestral rela- 

 tion to the other. 



If Professor Cope's hypothesis be correct we should naturally 

 expect to find a series of forms connecting the two groups and 

 leading to a common term, showing how the large and most 

 curious Dinocerata could be closely related to the smaller and 

 much less striking Coryphodons. In the latter there is a com- 

 plete set of upper incisors and a canine tusk of moderate 

 size ; the lower incisors possess but a single lobe and the lower 

 canine is erect and as large as the upper tusk, which it opposes. 

 In the Dinocerata the upper incisors are entirely wanting, the 

 canine is converted into a great sabre-like tusk ; while the lower 

 canine is very small, shaped like the incisors and functionally 

 belonging to the latter, which present the extraordinary peculi- 

 arity of having compressed bilobed crowns. In the Corypho- 

 dons the cranium is nearly flat on top, there being no sagittal 

 crest, and there are none of the great osseous protuberances 

 which give such a characteristic and peculiar appearance to the 

 skull of the Dinocerata, although in some species of Corypho- 

 don (e. g. elephantopus) there are small swellings which in- 

 dicate these protuberances ; there is also a. beginning of the 

 supra-occipital and parietal crests which in Uintatherium reach 

 such great proportions. The nasals are thin, short and weak, 

 ending anteriorly in a point and strikingly different from the 

 very long and heavy nasals of the Dinocerata. 



The only form hitherto known which in any way helps to 

 fill the gap between the two sub-orders of the Amblypoda is the 

 genus Bathyopsis Cope, from the Wind river or lowest Bridger 

 beds of Wyoming. Of this genus only the lower jaw has 

 been found; but the important point is brought out that the 

 lower canine was a large erect tooth, probably opposing the 

 upper canine and not forming a part of the incisor series as is 

 the case in Uintatherium. The form and position of this tooth 

 make it exceedingly probable that the upper canine had not 

 reached the great sabre-like proportions found in the other Di- 

 nocerata. It is not certain whether the presence of the first 

 premolar is a constant feature or simply indicates a milk-molar 

 persisting longer than usual. The latter is so frequently the 

 case, that it is impossible to attach any value to its occurrence 

 in an isolated specimen. 



The Princeton Expedition of 1885 had the good fortune to 

 discover, in the Bridger beds of Henry's Fork, Wyoming, an- 

 other missing member of this hypothetical series. The new 

 ^enus. for which I propose the name fflachoceras, may be briefly 

 defined as follows : animals allied to Uintatherium, without 

 upper incisors, and having six molars of the Uintatherium 

 pattern, and large upper canine tusks ; but without nasal pro- 



