1916] 



Merriam: Fauna of Cedar Mountain Region 



183 



resent an animal larger than any of the known forms of HypoMppus, 

 but approaching in size HypoMppus a/finis, the largest described 

 species. They are absolutely larger than the permanent premolars of 

 H. osborni, and larger than the milk molars of the type specimen of 

 H. affinis. The excess in dimensions is evident in both the antero- 

 posterior and transverse diameters. 



In form and pattern the milk molars resemble in general the per- 

 manent dentition of HypoMppus osborni. 



The principal difference between the Nevada specimen, no. 21056, 

 and HypoMppus osborni is found in the separation of the outer end 

 of the metaloph from the ectoloph. In none of the milk molars of 

 the Nevada specimen is the summit of the outer end of the metaloph 

 connected with the ectoloph. In Dm 2 and Dm 3 the base of the met- 

 aloph scarcely reaches the base of the ectoloph. In each of these 

 teeth there is a small transverse ridge or tubercle pointing inward 

 from the ectoloph at the posterior end of the paracone crescent. This 

 transverse prominence arising from the ectoloph extends inward near 

 the outer end of the metaloph but fails to meet that ridge. The outer 

 end of the metaloph tends to swing a little in front of the inner 

 transverse prominence of the ectoloph. 



The inner transverse prominences arising from the ectoloph attain 

 their greatest elongation or height near the summit of the ectoloph, 

 and rapidly diminish in height as they extend toward the base of the 

 tooth. On Dm 4 the transverse prominence consists of two small tooth- 

 like projections. On the longer or lower of these points the diameter, 

 parallel with height of the tooth crown, is not more than twice the 

 anteroposterior diameter. The second projection, situated farther 

 toward the base of the ectoloph, is an exceedingly small tubercle. 

 The smaller projection does not reach the bottom of the valley between 

 the metaloph and the metacone crescent. On Dm 3 the inner transverse 

 prominence of the ectoloph is very small, and is situated near the 

 crest of the ectoloph. On Dm 2 the prominence is higher, but is 

 reduced rapidly at the proximal end and does not connect with the 

 metaloph. 



The Nevada form seen in specimen 21056 represents a type with 

 dentition in general close to that of HypoMppus, but distinguished 

 especially by the less advanced stage of evolution of the metaloph 

 in the temporary molars. 



Limbs. — Portions of both the anterior and posterior limbs (fig. 19a 

 and 196) exhibit some of the essential characters. The general 



