130 Annals of the Carnegie Museum. 



step towards the development of a posterior cross-crest, such as is 

 found in Trigonias oshorni from the base of the Oligocene. Deciduous 

 Py is present in the right ramus (see Fig. 19). My and My are much 

 worn, the crowns furnishing no detailed characters, while M^ practi- 

 cally agrees in all details with the same tooth of the known species 

 of the genus, except in its larger size. The ramus appears to be 

 proportionally slenderer than in Hyrachyus agrarius. Hyrachyus 

 princeps Marsh, which also is a large form, is smaller than the 

 specimen under description. If the specimen does not belong 

 to the latter species ^^^ it may be called Hyrachyus grande sp. nov. 

 simply to indicate its extraordinarily large size (See Figs. 18 and 19). 

 The specimen No. 31 12 is slightly larger than Hyrachyus agrarius 

 Leidy, and appears moreover to differ from the latter by a proportion- 

 ,ally greater development of the metaconid and a slight basal elevation 

 indicating the tetartoconid. 



Measurements. 



No. 2908. No. 3112. 

 Length of ramus from anterior point of symphysis to and in- 

 cluding M3 215 mm. 



Depth of ramus at Py 40 



Mg- 54 " 



Antero-posterior diameter of cheek-teeth 161 



" P^ 21 " 15 mm. 



Transverse " " " 15 " n 



Antero-posterior " " My 26 " 22 



Transverse " " " 19 " I4 



Subfamily AMYNODONTIN.F:. 

 Genus Amynodon Marsh (Plate XLVII, Figs. 5-7). 



Amer. Jour. Sci., Vol. XIV, 1877, pp. 251-252. 



This genus is represented by a number of individuals. The material 

 has a considerable range in size and undoubtedly represents two or 

 probably three species. Unfortunately the fragmentary condition 

 of the greater number of the specimens does not admit of an accurate 

 identification. The smaller individuals are therefore provisionally"® 



11^ There is unfortunately no other basis of comparison between these two speci- 

 mens besides M 3^. In H. princeps the cingulum of the anterior face is heavier and 

 the anterior extension of the metalophid is somewhat less developed than in the 

 Uinta specimen. These may or may not be valid characters. 



116 All the specimens referred to A. advenum are too small when compared with 

 the measurements of the type specimen by Marsh. One specimen in our Collec- 

 tion, No. 3217, is especially small and may represent a new species. 



