114 



OSBORN: OLIGOCENE, MIOCENE, PLIOCENE EQTJIDyE. 



Cope observes (1SS9, p. 450): "The specimen No. 1 equals that of //. spcciosum in dimensions; No. 2 is a little 

 larger." These cotypes have not been identified; the species therefore rests on specimen No. 1. 



Cope gave the following measurements for specimen No. 2, a third superior premolar: longitudinal .028, anteropos- 

 terior, .025, transverse at column .014. A right superior molar. Measurements: longitudinal .019, anteroposterior .022, 

 transverse at column .022. This specimen has not been located in the Cope Collection (1917). 



Characters. — (Osborn, 1918) (1) Type premolars with measurements as cited by Gidley above; (2) crowns of inter- 

 mediate length, hypsodont; (3) protocones relatively narrow, suboval, with a spur tending toward protoloph; (4) enamel 

 plications of protoconule consisting of two double folds in the crochet region; (5) enamel plications of metaloph and of 

 hypostyle region complex. 



The double plication of the pli caballin seems to distinguish this form from the M. scvcrsu-s, M. paniensis, and M. 

 relictus types. Similar double enamel folds of the pli caballin are observed in the types of M. calamarius and M. repub- 

 licanus from the Lower Pliocene of the Santa Fe marls of New Mexico and of the Republican River, Nebraska, Procamelus 

 zone. 



Ncotypc. — Osborn (1918) rejects Cope's cotype (specimen 2, Plate 15.1) as belonging to a different species from the 

 type, and selects as a ncotypc the skull Princeton Mus. 12291 (Plate 12), which agrees closely with the type of M. sphenodus 

 (Plate 15.2) in the proportions of p 2 " 3 and in the double pli caballin, pli prefossette, and pli postfossette, which are all 

 progressive characters. This neotype (Princeton Mus. 12291) is recorded from the " lower levels of Pawnee Creek beds," 

 as found west of Sand Canon, Horsetail Creek drainage, Logan County, Col. 



Merychippus campestris Gidley, 1907. 



Plates 15.4,5, 19.3,4, 26.1, 44.1, 49.1, 50.3,7. Text Figs. 88, 89. 



Merychippus campestris sp. nov., Gidley, J. W. "Revision of the Miocene and Pliocene Equidae of North America," Bull. Amer. 

 Mus. Nat. Hist. Vol. XXIII, Art. XXXV, Nov. 26, 1907, p. 928, no figure. 



Horizon and locality. — Pawnee Buttes, Pawnee Creek formation, Colorado, Merychippus zone, Middle Miocene. 

 Type collected by W. D. Matthew of the American Museum Expedition of 1898. 



Type. — Amer. Mus. 9096. " Upper molar-premolar series of the left side associated with the lower jaws, fragments 

 of skull, vertebra?, and portion of fore and hind limbs and feet." Measurements: (Gidley) superior molar-premolar series 

 .1445; p 4 a.p. .023, tr. .0255; m 1 .0205, tr. .024; length of Mtc. Ill .175; length of femur .244; length of tibia .275. 



Type figure— Plates 15.4, 19.3, 44.1, 49.1, 50.3,7, text Figs. 88, 89. 



Characters. — (Gidley, 1907, pp. 92S, 929) (1) Superior molars of the same general appearance as those of Pliohippus 

 spectans Cope, but differing in the following characters: (2) the molars with shorter crowns; (3) external cones (pa, ma) 

 thicker transversely, making less transverse width for the fossettes; (4) protocone smaller and more rounded, being nearly 

 circular in outline; (5) as in P. spectans the horns of the fossettes end in broadly open loops; (6) the enamel borders are 

 very simple throughout. (7) Lower jaws comparatively long and slender. (8) Mtc. Ill moderately short and heavy, 

 lateral metacarpals very much reduced. (Osborn, 1918) (9) Enamel plications very simple; (10) protocone extended 

 inward more than hypocone, suggesting some of the simple Pliohippus types of molar. 



(Matthew, 1913) A referred skull and jaws, Amer. Mus. 9459, with old teeth, gives important comparative characters. 



Merychippus eoplacidus sp. nov. 

 Plates 20.1, 39.6, 44.2, 47.1, 49.2, 54.2. Text Fig. 90. 



Horizon and locality. — Pawnee Creek beds, Pawnee Buttes, northeastern Colorado. Middle Miocene. Type col- 

 lected by F. B. Loomis, of the American Museum Expedition of 1901. 



Type. — Amer. Mus. 9347. Lower jaw, cervicals, fore and hind feet, humerus, ulno-radius, parts of femur and tibia, 

 all of one individual. 



Type figure — Plates 20.1, 39.6, 44.2, 47.1, 49.2, 54.2, text Fig. 90 of this Memoir. 



