20 GEOLOGICAL SURVEY OF TEXAS. 



sponding one iii the type specimen should be. The latter should meas- 

 ure about 205 mm., whereas the length of the tooth now described is 

 only 140 mm. It may pertain to a different species, but for the present I 

 refer it to a small race of the T. serridens, under the name of T. serridens 

 cimarronis. 



This tooth was found alone, but other remains of Mastodons are not 

 rare in the formation, some of them indicating large individuals. 



DIPLARTHRA. 

 APHELOPS, Cope. 



Proceeds. Amer. Piiilos. Society, 1873, p. 520. 



Remains of this genus we found to be rather rare, but three individu- 

 als having come under our notice. Two of these are represented by badly 

 damaged teeth, not yet determined, while another is represented by a 

 skull of the species mentioned below. 



APHELOPS FOSSIGER, CopC. 



Bulletin U. S. Geol. Survey Terrs. 1878, p. 382; Amer. Naturalist, 

 1879, 771h., figs. 3 and 6; 1887, p. 1006, fig. 22. 



A skull of this species was obtained, which does not differ from those 

 previously known from Nebraska and Kansas. 



PROTOHIPPUS, Leidy. 



Proceedings Academy of Philadelphia, 1858, p. 56, name only. Ex- 

 tinct Mammalia of Dakota and Nebraska, 1869, p. 275, first desci'iption. 

 Cope, Bulletin U. S. Geol. Survey Terrs., No. 1, Jan., 1874, pp. 10-15. 



Merychippus, Leidy, Proceed. Phila. Academy, 1858, 27 (defined), 

 partim. Extinct Mammalia Dakota and Nebraska, 1869, 292 (deciduous 

 dentition). 



Parahippus, Leidy, op. cit., 1858, p. 26; Extinct Mammalia, etc., 1869, 

 314 (deciduous dentition). 



HypoMppus, Leidy, op. cit., p. 26; Extinct Mammalia, etc., p. 311 (de- 

 ciduous dentition). 



Protoliippus s. Merychippus, Leidy, Report U. S. Geol. Survey Terrs., 

 4to.,I, p. 322. 



Interior columns of the superior molars united to the inner crescents, 

 their worn sections forming loops of the internal border of the crescents. 

 Second and fifth digits present on both limbs and of reduced size. Bi- 

 cipital groove double. Metapodials without trochlear keel anteriorly. 



The genus is like Hippidium in dentition, and like Hippotherium in the 

 structure of the feet. Its principal distribution is North American, where, 

 it is confined, so far as yet known, to the Loup Fork beds, 



