MERYCHIPPUS. 



101 



Merychippus seversus Cope 1878. 



Plate 13.8, 17.1. Text Fig. 74. 



Stylonus seversus, gen. et sp. nov., Cope, E. D. "On Some of the Characters of the Miocene Fauna of Oregon," Proc. Amer. Philos. 

 Soc. Vol. XVIII, 1878-1880 (sig. dated Dec, 1878), p. 7G, no figure. Palceontological Bull. No. 30, "Dec. 3, 1878." Hippotherium 

 seversum Cope, "A Review of the North American Species of Hippotherium," P. A. P. S., Vol. XXVI, June, 1889, pp. 457, 458, fig. 24, 

 24a, 



Horizon and locality. — Mascall formation of Cottonwood Creek, Ticholeptus zone, Grant County, Oregon. Type 

 collected by J. L. Wortman. 



Type. — Am. Mus. 8180. (Cope, 187S, p. 76) "Two superior molar teeth were accompanied by a number of inferior 

 molars as having been all found together, but whether they belong to one individual is uncertain." (1889) i' ... II. seversum 

 was originally described from a superior molar, which though worn over the entire grinding face of the crown still retains 

 the posterior column [hypocone] distinct from the posterior inner crescent." (Gidley, 1907, p. S97) "A right upper molar 

 tooth, ?m 2 , Amer. Mus. S1S0." Measurements: (Gidley) nr a. p. .0175, tr. .0165, height of crown .028 outside, .016 inside. 



Type figure. — Text Fig. 74 of this Memoir. 



Fig. 74. Original figures of the superior molar of the type of Merychippus seversus Cope, Am. Mus. 8180. Natural 

 size. After Cope, 1889, figs. 24, 24a. 



Characters. — (Cope, 18S9, p. 457, Osborn, 1918) (1) Crown of superior molar moderately elongate [hypsodont], 

 curved; (2) section of anterointernal column [protoeone] an elongate oval with an anterior spur directed toward the internal 

 median group [protoconule]; (3) posterointernal column [hypocone] also elongate oval in section, distinct from postero- 

 internal crescent [metaconule] ; (4) crescents [protoconule and metaconule] separated by wide lakes [fossettes] entirely 

 filled with cement; (5) borders of metaconule crescent ptychoid, protoconule crochet junction with pli caballin; (6) ecto- 

 loph without median paracone and metacone. 



Among the referred specimens from the Mascall are Amer. Mus. 8181, 81S2. It should be compared with M. spheno- 

 dus, from a somewhat later horizon, which it antedates. 



Merychippus isonesus Cope 1889. 

 Plates 6.8, 10.4, 13.1,2, 17.3,4, 42.1,2. Text Figs. 75, 77. 



Hippotherium isonesum Cope. "A Review of the North American Species of Hippotherium," Proc. Amer. Philos. Soc, Vol. XXVI, 

 1889, (sig. dated June 5, 1889), pp. 451-457, fig. 23. This type was originally referred to as Hippotherium seversum Cope, Cope, E. D., 

 [Named and listed] "On Two New Species of Three-toed Horses from the Upper Miocene, with Notes on the Fauna of the Ticholeptus 

 Beds," Proc. Amer. Philos. Soc, Vol. XXIII, April, 1886, p. 359. Not Vol. XVIII, 1878, p. 76. 



Horizon and locality. — Mascall formation of the John Day series, Cottonwood Creek, Oregon, Ticholeptus zone. 

 Type collected by J, L. Wortman, 



