Troxell — Dicer atherium and the Dicer atheres. 205 



rocone, and the shape of the medifossette inclosed, in 

 P^-*, by a mure. As in D. annectens, P^ is subqnadrate, 

 but the protoloph is less prominent and does not extend 

 beyond the metaloph. The anterior portion of the 

 ectoloph is not so prominent on any of these premolars, 

 but in P^ it is unusually subdued. A small internal 

 basal cusp may be seen on this tooth also. P^-* each show 

 the mure joining the two inner lophs. On these teeth 

 the crochet is situated well out on the metaloph ; it is not 

 directed forward but inward toward the slender crista 

 as though in anticipation of a continuous wall in later 

 forms. 



In each premolar the metaloph is compressed and very 

 narrow between the central and posterior fossae. The 

 medifossette itself approaches a cylinder in form in that 

 the sides are nearly parallel vertically; this marks a 

 beginning of hypsodonty, and is a character to be noted 

 in Menoceras cooki and other Miocene diceratheres. 



In this species the posterior nares extend forward to 

 the first molar. 



Measurements of Holotypes. 



D. armatum D. lobatum D. annectens D. cuspidatum 



No. 10003 No. 12487 No. 10001 No. 12007 



Y.P.M. Y.P.M. y.P.M. Y.P.M. 



mm. mm. mm. mm. 



P, ant.-post. diameter 34* 20 23 



P^ length, ant.-post 29 24 20 n9 



Width, transverse 27 21 18 



P^ length 33 31 24 24 



Width 39 36 29 30 



P^ length 39 38 29 28 



Width 47 47 35 36 



P^ length 40 39 29 30 



Width 51 52 37 39 



M^ length 52 53 39 



Width 53 54 41 



W, length 55 42 



Width 57 54 43 



M^ length 47 34 



Width 50 37 



Molar-premolar length 254 ?190 



Molar series, length 144 105 



Premolar series, length .... 129 ?97 



* Measure of plesiotype, No. 10005, Y. P. M., fig. 1 A. 



