FAUNA OF THE EQUUS BEDS. 81 



ferior molars with a fragment of lower jaw (No. 35); two inferior with 

 part of a superior molar (No. 39); molars lots 2, 4 and 49, and a sym- 

 physis mandibuli with incisors (No. 12). 



Tlie inferior molars display the characters already pointed out under 

 the head of the E. simplicidens (page 66). They may be distinguished 

 from those of that species by the wide and deep channel of the internal 

 face of the crown, which is due to the wide divergence of the metaconid 

 from the metastylid ; in this respect resembling the small species E, eurys- 

 tylus and E. minutus. The greater approach to isolation of the entostylid 

 also distinguishes them from those of E. simplicidens. 



Leidy united with this species' his Equus occidentalis* . In my synopsis 

 of the American species of this genus, f I have retained them as distinct 

 on the ground of the smaller size of the protocone in the latter. It is, 

 however, the fact that the diameter of this column is frequently less on 

 the premolar than the molar teeth in this genus, although not always. 

 The types of Leidy' s description display this character in a marked de- 

 gree, and I have not observed it in the numerous specimens that have 

 come under my notice from the Staked Plains, while it is to be observed 

 in a majority of the teeth from the beds of the Oregon desert. Transi- 

 tions between the two types are not rare, and may be seen in passing 

 from the front to the back part of the full series in a skull described by 

 me from southwest Texas. + See Plate XXII, Fig. 3. 



The symphysis mandibuli repeats exactly the characters which I as- 

 signed to that of the E. occidentalis in my paper above cited (page 11). 

 That is, the mental foramen issues entirely anterior to the posterior 

 border of the symphysis, and not entirely or partly posterior to it, as in 

 E. caballus. The canine is separated from the external incisor by a 

 shorter symphysis than in the E. caballus, resembling in this respect the 

 quagga. The symphysis is a little shorter in the Texas than in the 

 Oregon specimen. 



A remarkable molar (No. 12, July 19), exhibits an unusual peculiarity. 

 The hypocone embraces posteriorly tb,e enamel fold which separates it 

 from the metaconule, so that it becomes a columnar tube, and its section 

 on the grinding face an oval area. The position is remarkable, being 

 immediately posterior to the internal half of the posterior lake, instead 

 of entirely interior to its internal margin, as is the usual position of the 

 inflection. This is probably due to the fact that this molar is the last one 

 of the series. In addition to this column there is a similar, but smaller, 

 one just posterior to the external bone of the posterior lake, which does 

 not extend so far posteriorly as the larger column already described. 



*Report U. S. G. Survey Terrs., 1, 1873, p. 242. PI. XXXIII, Fig. 2. 

 tProceeds. Amer. Philosoph. Soc, 1884, p. 10. 

 {American Naturalist, 1891, p, 912. 

 6-GeoI 



