HYRACHYUS. 661 



Six of the above species have come nnder my observation, together 

 with two others of whose generic position I am not certain. One of these 

 IS quite small and is probably the H. nanus of Leidy, which is said by 

 Messrs. Scott, Spier, and Osborne to have only six inferior molars. My 

 specimens are not sufficiently complete to indicate whether the species 

 should be referred to Pachjnoloplms, which possesses that formula, or not. 

 The second is intermediate in size between H. nanus and H. crassidens, and 

 I have identified it with the Hyrachyus hoops of Marsh. Messrs. Scott, Spier, 

 and Osborne state that that species has no diastema, and on this account 

 they refer it to a distinct genus for which they employ the name Helaletes 

 Marsh. My specimen does not enable me to verify these references. 



Hyrachyds princeps Marsh. 



American Journ. Sci. ami Arts, 1872, p. 125. 

 Plate LII; fig. 4. 



This, the largest species of the genus, is represented in my collection 

 "by the superior molar tooth of an adult specimen, Plate LII, fig. 4; and 

 Ity a part of the mandibular ramus of another individual of immature age. 

 Both the specimens were found by myself on South Bitter Creek, Wyo- 

 ming, in beds of the Bridger epoch, of the Washakie basin. 



Hyrachyus sp. 



I Hyrachyus eximiua pt. Leidy Report U. S. Geol. Surv. Terrs. I Plate XXVI, figs. 9-10. 



Portions of mandibles of two individuals are too large to be referred 

 to the H. eximius, and are considerably less in proportions of the teeth than 

 those of H. princeps. They may belong to the H. imperialis of Scott, Spier, 

 and Osborne, although the measurement of the second inferior molar, the 

 only tooth of that series described by those authors, somewhat exceeds that 

 of my specimens. I give these for comparison. 



Measurements. 



M. 

 No. 1. No. 2. 



Length of three true inferior molars 060 .060 



Length of second true molar 021 .022 



Width of second true molar 015 .014 



Depth of ramus at second true molar 045 ,03^ 



