24 GEOLOGICAL SURVEiY OP TEXAS. 



True molars 72 mm.; i)riiicipal premolars 80 mm.; fourth 



premolar one-rooted; facial edge acute. .P. mirabllis 



IV. Preorbital region itnknown; 

 Principal premolars 59 rara.; fourth two-rooted; enamel sim- 

 ple; paracone cylindric .-P. labrosud 



Lakes transversely extended; borders plicate but without 

 special loop of the anterior lake; iuteirnal columns small^ 



sitbdyliildi'ic; molars 21 by 23 mm , . . . ,P. dastitli 



Lakes narrower; borders plicate in young; the loop of the 

 anterior long persistent; internal columns with ovrtl section; 



crown averaging 15x17 mm. . < . . . i , P. placidm 



In the species in which that part of the cranium is known, there is a 

 longitudinal fossa above the position of the preorbital fossa, extending 

 along the adjacent parts of the nasal and maxillary bones. That is, it is 

 present in the P.pachyops, P. fossulatus, P. sejunctus, P. insignis, and P. 

 mirabilis. 



Species in which the protocone does not unite with the paraconule 

 until late in life, are the P. placidus, P. lenticularis, Cope (described in 

 the supplement to this chapter), and P. supremus, Leidy, Exti Mammalia 

 Dak. and Nebr., p. 328, pi. XXVII, figs. 3, 4. 



Before decrlbing the species contained in the collections made by the 

 Geological Survey of Texas, I enumerate the species, and offer such re- 

 mai'ks on them as may be appropriate. 



Protohippus pachyops, Cope, sp. nov. infra. 



Protohippus perditus, Leidy, Extinct Mammalia of Dakota and Ne- 

 braska, 1869, 275, pi. XVII, figs. 1, 2 (young adult) ; Report U. S. Geol. 

 Survey Terrs. , I., 1873, 248, pi. XX, fig. 16. Parahippus cognatus, Leidy, 

 Extinct Mammalia, etc., p. 311, pi. XXI, figs. 7-10 (unworn deciduous 

 molars). Protohippus profectus, Cope, Proceed. Amer. Philos. Society, 

 1889, p. 447, pi. II, figs. 9-12. 



Of this species the most important specimens in my collection are the 

 following: Two right maxillary bones with full sets of molars of adult 

 but not old animals from northeast Colorado, collected by myself; part 

 of maxillary with four molars and a part of the skeleton from north- 

 ern Kansas, Dr. R. H. Hill; nearly all the molar teeth of both" sides, with 

 considerable part of skeleton from Hitchcock county, Nebraska, F. Hazard ; 

 right maxillary bone with facial region and four molars, from same local- 

 ity and collector; numerous loose molar teeth of another individual, same 

 locality and collector; numerous isolated molars, mostly from Colorado. 

 Deciduous dentition, part of the molar series from northeast Colorado, 

 E. D. Cope; entire series In maxillary bone from Laramie Peak, W3'0- 

 mlng, J. C. Isaac. 



