MESOHIPPUS. 



43 



Type. — Ottawa Mus. 6297, an imperfect left upper molar. Measurements: height of protoeone, .0047. 

 Type figure. — Text Fig. 24 of this Memoir. 



Characters. — (Lambe, 1905) "This tooth is about the size of, or possibly smaller than, M. westoni, but is more pro- 

 gressive in every way. There is an entire absence of an internal cingulum, the cross crests are better developed and rela- 

 tively 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 protoloph and connects closely with the forward slope of the paracone. The hypocone has about the same 

 height as the protoeone. The anterior cingulum is strong." 



Lambe observes (op. eit. p. 51) that M. prweocidens is nearly related to and more advanced than M. westoni Cope or 

 M. montanensis Osborn of the Titanotherium zone. 



Mesohippus propinquus Lambe, 1905. 

 Text Fig. 24(15,16). 



Mesohippus propinquus, sp. nov., Lambe, Lawrence M. "Fossil Horses of the Oligocene of the Cypress Hills, Assiniboia," Trans. 

 Roy. Soc. Canada, 2nd Ser., Vol. XI, Sec. IV, 1905-1906, issued Aug., 1905, p. 47, PI. ii, figs. 3, 4. 



Horizon and locality. — Oligocene deposits capping the Cypress Hills, Assiniboia, Titanotherium zone to Leptauchenia 

 zone. This type is regarded (Lambe) as of Oreodon zone age. Type collected by Lambe. 



Type. — Ottawa Mus. 6298, second right upper premolar, worn, p 2 (PI. ii, fig. 4). Measurements: p 2 a.p. .013, tr. 

 .0135. Cotypcs. Second left upper molar, Ottawa Mus. 6290 (PI. ii, fig. 3); second right upper molar, unworn, 

 Ottawa Mus. 6291. 



Type figure. — ■ Text Fig. 24 of this Memoir. 



Characters. — (Lambe, 1904, pp. 47-48) Type. Closely allied to and resembling M. bairdii although distinct, slightly 

 larger and more primitive than M. bairdii, proportions different. Cotype. "In the unworn tooth, Fig. 3 (left upper m 2 ), 

 the ectoloph is well elevated above the cross crests in which the protoeone and hypocone are conspicuously higher than 

 the conules. The hypocone exceeds the protoeone 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 con- 

 nects with the protoloph, and the ribs are faintly shown. There is no trace of an internal cingulum." 



Lambe regards M. propinquus as nearly related to and more primitive than M. bairdii of the Oreodon zone. 



Mesohippus stenolophus Lambe, 1905. 

 Text Fig. 24(18,19,20). 



Mesohippus stenolophus, sp. nov., Lambe, Lawrence M. "Fossil Horses of the Oligocene of the Cypress Hills, Assiniboia," Trans 

 Roy. Soc. Canada, 2nd Ser., Vol. XI, Sec. IV, 1905-1906, issued Aug., 1905, p. 48, PI. ii, figs. 6, 6a, 6b. 



Horizon and locality. — Oligocene deposits capping the Cypress Hills, Assiniboia, Titanotherium zone to Leptauchenia 

 zone. This type is regarded as of Leptauchenia zone age. Type collected by Lawrence M. Lambe. 



Type. — Ottawa Mus. 6302, first left upper molar, unworn. Measurements: m 1 a.p. .014. Cotype. M 3 , right, 

 Ottawa Mus. 6302. Measurements: a.p. .0125, tr. .015. 



Type figure. — -Text Fig. 24 of this Memoir. 



Characters. — (Lambe, 1905, pp. 48-49) "These teeth represent an apparently undescribed species of Mesohippus 

 larger than M. brachystylus, but resembling it in some particulars. The differences noticed are: (1) the greater relative 

 size of m 3 with a more pronounced obliquity of the cross crests in these teeth; (2) the greater length of the metaloph, which 

 in ?;/ 3 is connected with the ectoloph, and (3) the intimate connection of the hypostyle with both the posterior cingulum 

 and the metastyle. The resemblances are: — (1) somewhat similar general proportions with about the same degree of 

 development of the protoconule and a like suppression of the metaconule; (2) the parastyle and internal cingulum simi- 



