44 Troxell — Hyrachyus and its Subgroups. 



specimen (in pi. I, about one thirteenth nat. size). The 

 posture selected for the restorations is that of an 

 extreme phase of a fast trot, with alternate front 

 and hind feet advanced, the whole purpose being to 

 emphasize the idea that this is a light, agile animal, 

 a cursorial rhinoceros. The missing parts were restored 

 in plaster and the bones arranged on the flat base; the 

 position of each was carefully worked out by the study 

 of other skeletons, photographs, and observations on 

 living animals. 



This interesting specimen, found probably in the early 

 seventies, drew the attention of Professor Marsh, who 

 apparently intended to make it the type of a new species ; 

 his observations follow, but of course the species name, 

 here quoted from his manuscript, has no standing : 



"Notes on Hyrachyus bairdi M. 



"No. 1170. Skull and skeleton nearly complete (H. Fork, 

 Wy.). 



"1. Hind feet longer and stouter than fore feet. (Reverse 

 true in tapir.) Metatarsals curved. 



"2. No supratrochlear foramen in humerus (as in tapir). 



"3. Navicular sesamoids present, but minute, in all three toes 

 behind, and at least II, III and IV in front. (Not present in 

 tapir or rhinoc.) 



' ' 4. Ulna smaller than in tapir. ' ' 



Additional points on the new type. — The dental for- 

 mula is 3. 1. 4. 3. P 2 has a strong cross ridge anteriorly 

 like the larger premolars; it is slightly wider (8.7 mm.) 

 than it is long (8 mm.). P 3 - 4 are very similar in propor- 

 tions; the latter is larger. P 1 was probably as wide 

 transversely (6.4 mm.) as it was long; the anterior part 

 is broken away. The lower premolars show a gradual 

 change from the first to the fourth. F ± has a single cusp 

 with a small internal ridge leading from the apex; P 2 

 shows an antero-internal groove set off by what may be 

 called the paraconid; P 3 . 4 both have the two cross 

 crests and, the latter especially, take on the form of a true 

 molar. 



The molars increase gradually in length from the first 

 to the third, but change very little in width. There is 

 practically no difference in height between the anterior 



