134 



OSBORN: OLIGOCENE, MIOCENE, PLIOCENE EQUID.E. 



apparently referable to it [Protohippus placidus] are as follows: 1. A first upper molar tooth [p 2 ] about half worn away. 

 The masticating surface, represented in figure 40, plate XVIII, presents extreme simplicity in the arrangement of the 

 enamel, compared with its condition generally in equine animals." This tooth [fig. 40] is the type. Measurements: 

 (Gidley, 1907) p 2 a.p. .0185, tr. .016. (Leidy) Height of crown external 9 to 10 lines. The other specimens, figs. 39, 41- 

 48, are paratypcs, there being no evidence in Leidy's description that these isolated molars were collected from the same 

 locality. The species thus rests on the very uncertain evidence afforded by the type second upper premolar (fig. 40). 

 Neotype. — (Gidley, 1907) Amer. Mus. 10830, a right maxilla, containing p L m 3 , also other upper and lower jaws, referred, 



Fig. 107. Neotype (Gidley) of Protohippus placidus Leidy, Amer. Mus. 10830. Portion of right maxilla with grind- 

 ing teeth, p'-m 3 , side and crown views. One-half natural size. Drawing by B. Yoshihara. 



from the Big Spring Canon and the Little White River exposures of South Dakota. Gidley (1906, p. 141) does not specify 

 Amer. Mus. 10830 as a neotype, but gives a clear and full definition of the species from this new material, first mention- 

 ing the maxilla, Amer. Mus. 10830, but including upper jaws Amer. Mus. 9830, 10S26, 10843, and lower jaws 10849, 

 10850a, 10853, 10855, 10857. 



Type figure. — Text Fig. 106 of this Memoir. 



Characters. — (Leidy, 1869) (1) Separated from P. perditus as an animal of small size. (2) Enamel plications in 

 the type and some of the paratypes relatively simple; (3) crowns less curved than in P. perditus; (4) central lakes [fosse ttes] 

 wide and gaping. 



