50 

 HYRACHYUS IMPERIALIS, sp. nov. 



Established on the second and third molars of each upper 

 jaw, and three premolars, and one lower molar, portions of 

 the skull and vertebras. 



This species is, with the exception of H. princeps, (Marsh), 

 the largest species of the genus as yet known. It differs from 

 H. princeps in the greater proportionate length of the molars, 

 in their larger size, compared with the bulk of the animal, and 

 in the less separation of the anterior external conical buttress. 

 The third molar is the largest ; the fold extending from the 

 antero-external lobe into the valley is very conspicuous. The 

 basal ridge (which is very strongly marked on the posterior 

 edge), is very feebly indicated on the exterior. The trans- 

 verse crests are more oblique in the second than in the third, 

 but in the latter the valley is deeper and the crests slightly 

 longer. The anterior conical buttress is of great size, being 

 larger than the anterior lobe. The premolars have, as usual, 

 one internal cone ; the anterior and posterior external lobes 

 approach close together, while the accessory fold from the 

 anterior lobe becomes very prominent, reaching the internal 

 cone and enclosing a valley between itself and the transverse 

 crest, The basal ridge does not extend around the inner 

 part of the crown as in H. agrarius. 



The only lower molar we have, seems to be a penultimate 

 molar of the right side. The basal ridge is large anteriorly, 

 very short posteriorly, but does not appear at all upon the 

 sides, as in H. agrarius. 



The remaining bones of the skeleton indicate a rather 

 small animal, the teeth are therefore proportionately very 

 large. 



The occipital condyles are small and sessile ; they are 

 much extended laterally, and the external angles are pointed. 

 In other respects they resemble the condyles of Palceosyops. 

 The zygomatic arch is slender and does not curve outward 

 strongly. We cannot tell how far the malar encroaches upon 

 the face. After leaving the maxillary it becomes much com- 

 pressed ; it has no post-orbital process. The maxillary is of 

 unusual breadth, extends far backwards, and it forms the 



