243 



River, and on the Niobrara River, Nebraska, which I referred to a species 

 with the name of E. excehus. A characteristic specimen referred to the latter 

 consists of a portion of the upper jaw containing the back four molars, repre- 

 sented in Fig: 31, Plate XXI, of the work last named. The teeth in this 

 specimen are so nearly identical in character with those from California, 

 referred to E. occidentalism as may .be seen by comparing the figure with 

 Figs. 1, 2, Plate XXXIII, of the present work, that there can be little doul)t 

 of the two named species being the same. 



Since the original description of the two specimens referred to E. occiden- 

 talism I have seen others of half a dozen ditferent individuals from California. 

 All these present sufficient correspondence in peculiarity of character as to 

 render them fairly representative of an extinct species, for which the name 

 of E. occidentalis is appropriate. Fig. 1, Plate XXXIII, represents a series 

 of the anterior four upper molars contained in a jaw-fragment. Tlie speci- 

 men, together with another similar one fiom a second individual, and contain- 

 ing all the molars except the last one, were obtained by Dr. George H. Horn 

 from an asphaltum deposit near Buena Vista Lake, California, and presented 

 to the Academy. Similar specimens have also been submitted to my exam- 

 ination, obtained at the same locality by Professor Whitney. 



The upper molar teeth of E. occidentalis are about the size of those of the 

 larger varieties of the domestic horse. From them they arc in general 

 readily recognizable l)y the greater simplicity in the course of tlie enamel 

 lines, as displayed on the worn triturating surface, and in the absence of the 

 small enamel-fold, directed inwardly, at the bottom of the oblique valley 

 between the inner principal folds of the crown, in wliich point these teeth 

 accord w'ith those of the existing ass. 



The measurements of the specimens referred to E. occidentalis and repre- 

 sented in the figures are as follows : 



Specimen of Fig. 1. 



Diameter of first molar . . 

 Diameter of second molar 

 Diameter of third molar . , 

 Diameter of fourth molar. 



