Peterson: Material Discovered in Uinta Basin. 101 



acters took place. ''^ Such an hypothesis makes it possible to admit 

 that the sudden appearance in a given horizon of the remains of new 

 forms more or less like those of the indigenous species, and sometimes 

 the actual mingling of them in the same geological horizon, represent 



Fig. i6. Diagram expressing the relationship of the HypertraguHdae. 



invasions, which gradually filled the places formerly occupied by an 

 older fauna. 



FERISSOBACTYLA. 



Subfamily Hyracotheriin^. 



Genus Epihippus Marsh. 



30. Epihippus gracilis IMarsh. (Plate XLIII, Figs. 4-8). 



Amer. Jour. Sci., Vol. II, 1871, pp. 37-38 (Anchitherium gracilis)/'* 

 This species is represented by five individuals all in fragmentary 

 condition. The best specimens, C. M. No. 2923 and No. 3398, each 

 consist of a few fragments of the skeleton. The specimens, especially 

 No. 3398, compare very closely with the description and illustrations 

 of Epihippus uintensis by Granger. The latter author, however, 

 was unable to distinguish between E. gracilis and E. uintensis.^^ 

 The accompanying illustration is given in order to further elucidate 

 the characters of the species (See Pis. XLII-XLIll). It is evident 

 that P- has the antero-external angle more acutely developed than 

 in the molars, which is due to some extent to the well developed 

 parastyle. The massive mesostyle of the molars answers well to the 

 description given by Granger. 



The glenoid cavity of the scapula is quite ovate in outline and the 

 coracoid process is prominent, -while the spine rises comparatively 



"Dr. W. D. Matthew, The Popular Science Monthly, Nov., 1910, pp. 473-478. 

 Acad, of Science, New York, Vol. XXIV, 1915, p. 100. 



'■• Later Professor Marsh established the name Epihippus which was published 

 in a foot-note in Popular Science Monthly, April, 1878, and Dr. O. P. Hay has desig- 

 nated the type, while Mr. Granger has recently pointed out the characters of the 

 genus (Amer. Mus. Nat. Hist., Vol. XXIV, 1908, p. 232.) 



^^L.c, p. 258, PI. XVIII, Figs. 4-5. 



