35 



Left upper molar {imperfect). Type. 

 Measurement in mm : — 



Height of protocone 4 - 7. 



The left upper molar, on which this species is founded, lacks the ectoloph and the pos- 

 terior border with the hinder slope of the hypocone, but is otherwise well preserved. 



This tooth is about the size, or possibly smaller than M. westoni, but is more progressive 

 in every way. There is an entire absence of an internal cingulum, the cross crests are better 

 developed, and relatively higher, with steeper slopes. The protoconule is relatively larger, and 

 the metaconule, although defined, scarcely breaks the continuity of the metaloph, which unites 

 in a decided manner with the ectoloph. The protoconule is distinctly defined in the proto- 

 loph, and connects closely with the forward slope of the paracone. The hypocone has about 

 the same height as the protocone. The anterior cingulum is strong. Mr. Gidley has informed 

 the writer that he " would expect to see the hypostyle well developed, were that portion of 

 the tooth present." 



Mesohippus propinquus, Lambe. 



Plate III, figs. 15 and 16. 



Mesohippus propinquus, Lambe, 1905. Fossil horses of the Oligocene of the Cypress hills, 

 Assiniboia; Trans. Royal Soc. of Canada, second series, vol. XI, section IV, p. 47, pi. 

 II, figs. 3 and 4. 



2nd right upper premolar, worn {figure 16). 



2nd left upper molar, unworn, {figure 15). Type. 



2nd right upper molar, unworn. 



The above teeth have been regarded by the author as characterizing a species of 

 Mesohippus distinct from M. bairdi, Leidy, although closely allied to it and most resembling it. 



They are of nearly the same size as those of M. bairdi, if anything slightly larger, and on 

 the whole more primitive. Their general proportions are somewhat different. 

 Measurements in mm. 



p 2 a.p 13 by tr. 13-5. 



m 2 left a.p 12 by tr .15 - 5, height of protocone 5. 



height of protocone 5'7, height of ectoloph. . . .8. 



m 2 right, a.p 12*2 by tr 15. 



In the unworn tooth, figure 15, (left upper m 2 ), the ectoloph is well elevated above the 

 cross crests, in which the protocone and hypocone are conspicuously higher than the conules. 

 The hypocone exceeds the protocone in height. The protoconule is well defined and distinctly 

 breaks the continuity of the protoloph. The metaloph is fairly continuous and shows a 

 disposition to unite with the ectoloph, which, however, it does not reach. The hypostyle is 

 connected at its inner end with the posterior cingulum and outwardly abuts against the 

 ectoloph ; it is of fair size. In the ectoloph the mesostyle is conspicuous, the parastyle is 

 flattened and connects with the protoloph, and the ribs are faintly shown. There is no trace 

 of an internal cinsrulum. 



& i 



Mr. Gidley has drawn the writer's attention to the interesting fact that the protocone 

 in these teeth "is peculiar in having the slope of its anterior face about equal to that of its 

 posterior face, while in M. bairdi, and all the middle and upper Oligocene horses, the anterior 

 face of the protocone is always much more abrupt than the posterior one." 



