Cope.] 4:b4 [Nov. 15, 



ably more complex than in the E. occidentalis. The internal anterior 

 column or protocone is remarkable for its great anteroposterior diameter 

 in the premolars as well as in the true molars, although in some of the 

 specimens figured by Leidy (I. c.) those of the p.m. ii and iii are not so 

 well marked in this respect as those in the specimens now described. In 

 the E. occidentalis, while this diameter is large in the true molars, it is 

 reduced in the premolars as it is in the E caballus. When the cementum 

 is wanting on the inferior molars, the surface of the dentine is seen to be 

 marked by fine longitudinal grooves. 



In the symphysis mandibuli preserved, the incisors are all present. 

 Their crowns all have considerably greater absolute and relative trans- 

 verse diameters than those of the E. cahallua, and the posterior cingulum 

 is present except in the external incisor, where no trace of it exists. I 

 have not observed this in the horse, but the inner wall of the cup is some- 

 times imperfect in the quagga. In the loose incisors preserved, which 

 are less worn than those in the symphysis, the internal wall of the cup is 

 not so well developed as in E. cabullus and E. occidentalis. Thus in four 

 teeth it is notched at the middle, and in two external teeth it has a wide 

 interruption, extending to the fundus in one, and nearly to the fundus in 

 the other. In this respect these teeth approach those of the E. fraternus. 



The last superior molar has a greater anteroposterior diameter than 

 usual, considerably exceeding that of the penultimate. Three such 

 molars display this peculiarity. 



In the characters of its molar teeth then this species is intermediate 

 between the E. major and E. occidentalis, and in the character of its 

 incisors it approaches E. fraternus. In order to learn more exactly of 

 its affinities it is necessary to make some comparisons with other portions 

 of the skeleton. For this purpose, among other parts, the occipital region 

 of one individual is available. 



This region differs from the corresponding part of the E. caballus, and 

 agrees in most respects with that of E. occidentalis.* A transverse crest 

 connects the paroccipital processes and the basisphenoid, bounding the 

 precondylar fossa in front, so as to convert it into a basin. In E. cabal- 

 lus and E. quagga this transverse crest does not exist, so that the fossa 

 opens directly anteriorly. The basisphenoid is not compressed as in 

 E. caballus, but is wide and robust, and the inferior face is marked by a 

 wide median groove. 1 have seen nothing like this in a true horse, but 

 the form is that of tiie E. occidentalis, where, however, there is no groove. 

 There is a longitudinal angle on each side of the sphenoid in the E. occi- 

 dentalis, which is wanting in /?. caballus, but of which a trace may be 

 seen in the E. fraternus. The condylar foramen in E. fraternus is more 

 anterior than in E. caballus, though this character will probably prove to 

 be less constant than the others mentioned. 



The E. intermedins is a shorter-nosed species than the E. caballus, the 

 distance from the anterior lower premolar forwards only equaling the 



"Proceeds. Amer. Phiios. Soc., 1884, p. 11. 



