MUSEUM OF COMPARATIVE ZOOLOGY. 157 



collection the well-preserved facial part of a skull, together with ihe lower 

 jaws ; hardlj' enough, however, to make the systematic position of the animal 

 entirely clear. The orbits are very large and deep-set, as in the tragulines, 

 and separated by a mere septum ; the lachrymals have a considerable extent 

 vertically, but extend little on the side of the face, and do not reach the nasals; 

 the maxillaries are proportionately higher than in Leptorneryx ; the nasals are 

 much contracted ; the palate is well arched from side to side, and the palatines 

 seem to be shaped much as in Tragulus ; the mandible is very slender. 



The last upper premolar is composed of an external and internal crescent, 

 enclosing a valley between them ; the third and second are very small and 

 apparently secant, without internal cusps ; the first, if present at all, was evi- 

 dently separated from the second by a considerable diastema. 



PERISSODAOTYLA. 



MBNODONTID^. 



MENODU9, PoMEL. 



Syn. Titanotherium, Leidy. Megacerops, Leidy. Brontotherium, Marsh. (1 Si/m- 



borodon, Cope.) Diconodon, Marsh. 



Generic Characters. — Dentition : I. | (variable), C. \, Pm. |^, M. f. The 

 incisors are small and variable in number. The upper and lower median in- 

 cisors are usually wanting. Molars and premolars alike, resembling those of 

 Chalicotherium in pattern. A stout pair of transversely placed horns devel- 

 oped from the frontals and nasals. 



There are three skulls in this collection and the horns of several others, rep- 

 resenting four or five species which may readily be distinguished. The chief 

 difficulty is in deciding where to draw the generic lines, which is increased by 

 the fact that the mandibles are seldom found associated with the skulls. As 

 in Uintatherium, the variability in the various portions of the skull, especially 

 in the region of the horns, is so extreme, that no two skulls are found which 

 are exactly alike. But the dentition, which is constant among the Dinocerata, 

 here greatly complicates the problems of classification. The premolars vary in 

 number, and the incisors, always of relatively small size, and fairly constant 

 in number in the upper jaw, vary from three to none in the lower jaw.* In 

 all the lower jaws found in Professor Cope's collection of Menodontidce from 

 Northern Colorado there are no incisors, and the mandibular symphysis is 

 extremely narrow. In the lower jaws of the Cambridge and Princeton collec- 

 tions, which are all from the Nebraska and Dakota exposures, the symphysis 

 is broad, and the incisors where preserved are two in number, while in one of 

 the Cambridge specimens no less than three incisor alveoli may be counted 

 upon one side of the symphysis. 



• One of the Cambridge skulls has but a single upper incisor, M. color adensis. 



