53 



A comparison of the nasals and horus of M. coloradensis, with those of Cypress Hills 

 species, is set forth in the table given below : — 



M. selwynianus. 



M. angustigenis. 



M. coloradensis. 



M. syceras. 



M. assiniboiensis. 



Nasals. 



Long and narrow, obtusely rounded 

 in front, under surface deeply ex- 

 cavated, lateral margins produced 

 downward. 



Thick and rather long, expanded 

 anteriorly, front margin very ob- 

 tusely pointed, under surface 

 moderately excavated. 



Of moderate length, thin and bent 

 downward anteriorly. 



Rather short, evenly rounded in 

 front, stout, shalTowly excavated 

 beneath. 



Very short and thick, ending square- 

 ly in front,under surface only slight- 

 ly concave. 



Horns. 

 Unknown ; probably short. 



Short, far apart, flattened at 

 base on anterior outer sur- 

 face, and cylindrical above, 

 directed decidedly outward. 



Of moderate length, cylindri- 

 cal above, flattened on pos- 

 terior outer surface at base, 

 directed obliquely outward 

 and upward. 



Lengthening, close together 

 and upright, more rounded 

 in section near base than in 

 M. angustigenis. 



Placed very far forward and 

 rather far apart; probably 

 long. 



A series seems to be represented here with selwynianus and assiniboiensis as extreme 

 forms, and coloradensis occupying an intermediate position. Compared with the type species, 

 selwynianus has long and narrow nasals, whilst those of assiniboiensis are broad and very 

 short. In angustigenis the nasals are rather long and the horns short. In syceras the reverse 

 is the case, the nasals are rather short and the horns are lengthened. Coloradensis has both 

 nasals and horns of medium length. A lengthening of the horns appears to have accompanied 

 a shortening of the nasals, and it is probable that selwynianus had short horns and assiniboiensis 

 long ones. Selwynianus, primitivus and assiniboiensis are, for the present, referred to the 

 genus Megacerops. 



A portion of a right maxilla, holding the second, third and fourth premolars, and a separate 

 left horn, are mentioned by Cope in the first part of this volume, under the name Menodus 

 americanus (Leidy), dimensions ^nd figures of the horn being given. Two separate horns 

 also belonging to the Cypress Hills collection of 1884, were referred by the same author in 

 the same publication to Menodus proutii (0. N". and E.). These two species are not determi- 

 nate, and the specimens referred by Cope to them do not present characters suflicient for 

 their identification with described forms. The horns evidently represent two species distinct 

 from Megacerops angustigenis and M. syceras. It is possible that, with the advent of new 

 material, they may be found to be assignable to two of the other three species of Megacerops 

 from the Cypress hills, viz., M. selwynianus, M. assiniboiensis and M. primitivus,o( 'which, the 

 horns are not known. 



