MUSEUM OF COMPARATIVE ZOOLOGY. 



159 



fessor Leidy * in 1873, and agrees closelj' with the corresponding portions of 

 the smallest skull in the Cambridge collection, both in form and measurement. 

 The skull is entire, and enables us to fully define this species. 



Dentition : I. L?L?> C. ^, Pm. ^, M. ^. No diastema behind the canine. 

 Second upper incisor sometimes wanting. First upper premolar small. Last 

 upper molar without distinct second cone. Upper premolars with a strong 

 internal cingulum. Anterior nares transversely broad and shallow vertically. 

 Nasals long and broad. Horns short and stout, obliquely compressed at the 

 base so that their faces point in three directions, erect and slightly recurved 

 when viewed from the side. The greatest diameter at the base is fore and aft. 

 Orbits large, and widely open. Superciliary ridge not prominent. Zygomatic 

 arches broad and powerful, but without flanges, Post-glenoid and post-tym- 

 panic processes separate or not broadly united. 



Figure 3. — Anterior portion of the skull of three species of Menodus, showing; the rela- 

 tions of the nasals to the horns in side view. 1. M. coloradensis. 2. M. tichoceras. 

 3. M. dolichoceras. 



The skull of this individual is considerably smaller than the type of M. 

 ingens, measuring only 27^ inches from the occipital condyles to the tips of 

 the nasals. The superciliary ridges expand into small postorbital- processes, 

 which are wanting in the above type. The post-glenoid processes do not 

 touch the post- tympanic. The M. ingens skull has two incisors, while this 

 specimen has but one. It is possible that one or more of the above differences 

 may prove to be of permanent specific value, but in the conformation of the 

 nasals and of the horns, as well as in all other details of proportion, these 

 skulls are apparently closely similar. 



In comparison with the type of S. trigonoceras, Cope, the horns and nasals 

 have somewhat similar proportions, but are less distinctly triquetrous at the 

 base. The skull also resembles that of M. angustigenis, Cope. 



M. tichoceras, sp. nov. This species may prove identical with S. altirostris, 

 Cope. Dentition : I. f , C. \, Pm. ^, M. S.t No diastema behind the canine. 



* Extinct Vertebrate Fauna, etc., U. S. Geol. Surv., Vol. I. Plate I. 

 t The number of lower incisors is inferred from the distinctly worn tips of the 

 upper incisors. 



