Troxell — Hyrachyus and its Subgroups. 43 



Hyrachyus affinis affinis (Marsh). 



(Fig. 3.) 

 Holotype, Cat. No. 12530, Y. P. M. Eocene (Bridger), near Grizzly 

 Buttes, one mile from Marsh's Fork, Wyoming. 



Marsh, in his first description (1871, p. 37), character- 

 izes this species by the small size, by the contour of the 

 crown of M 3 which has a deep notch in the posterior 



Fig. 3. 



125 30 TYPE Y. P. M. 



Fig. 3. — Holotype, Hyrachyus affinis (Marsh). Crown view of the molars 

 and fourth premolar. This is one of the smallest species of the genus. 

 Nat. size. 



margin of the base, and by the small, prominent antero- 

 external tubercle not closely connected with the adjoining 

 ridge. 



In addition to this, one notes the squared form of 

 the last molar, the rather weak posterior extension of the 

 ectoloph, the large second molar, and the weak metaloph 

 on the fourth premolar. 



Hyrachyus affinis gracilis, subsp. nov. 



(PL I and text fig. 4.) 

 Holotype, Cat, No. 11170, Y. P. M. Eocene (Bridger), Henry's Fork, 

 Wyoming. 



The type consists of a good skull and jaws, without 

 the anterior teeth, fore and hind feet and fore limbs, 

 together with parts of the hind limb bones, pelvis, ribs 

 and vertebrae. This specimen, previously on exhibition 

 for several years in the old Peabody Museum, has just 

 been remounted (see pi. I) on a large slab repre- 

 senting the original rock matrix; the preparation was 

 done by Mr. Hugh Gibb. Professor Lull has made a 

 restoration of the animal in the flesh in low relief, one- 

 fourth the natural size, modelled after the mounted 



