FOSSIL HORSE REMAINS FROM IDAHO — GAZIN 295 



noticeably narrow and sharply constricted along the median line. 

 The distance between the postglenoid and paroccipital processes is 

 shorter, accompanied by a more posterior and upward direction of the 

 external auditory tube, which passes through a higher and more 

 acute notch in the squamosal (see pi. 25, fig. 1). Moreover, the 

 periotic appears more crowded between the squamosal and exoccipital, 

 and the opening of the postglenoid or temporal canal is more obscured 

 than in E. grevyi. The bending of the cranium has also given the 

 line of the occiput a greater backward tilt, and the occipital crest is 

 much narrower and more sharply overhanging. 



In the facial region the skull is characterized by a prominent fossa 

 along the line of the naso-maxillary suture just anterior to the lachry- 

 mal bone. In some specimens, as in the type, there is also indication 

 of a slight fossa near the anterior margin of the jugal. In longitudinal 

 profile the skulls show a distinct dorsal concavity as in E. grevyi, 

 which in the fossils is immediately above the prominent facial fossae. 

 The width across the nasals at this point is less, but the depth of the 

 rostrum anterior to the dorsal concavity appears greater than in E. 

 grevyi and the width between the orbits appears greater. The naso- 

 frontal suture deviates considerably from a straight line, somewhat as 

 in E. caballus, much more than in E. grevyi, which exhibits an only 

 slightly inflected nasofrontal suture. The premaxillo-maxillary 

 portion anterior to the cheek teeth is elongate and relatively heavy 

 as in E. grevyi, and the anterior extremity is deep with the incisors 

 recurved as in that species, less procumbent than in individuals of 

 E. caballus of comparable age. The palate is noticeably broad in 

 specimens where this portion is not distorted by crushing, and in 

 many of the skulls the palatal surface of the rostrum appears more 

 sharply constricted immediately anterior to the cheek teeth (pi. 25, 

 figs. 2, 3), although the body portion of the premaxillae is as heavy 

 and wide or perhaps slightly v/ider than in Grevy's zebra. The nasal 

 process of the premaxilla is deep posteriorly, more so than is common in 

 E. caballus. The cheek teeth occupy a longer portion of the maxilla 

 than in E. grevyi, and the posterior extent of the cheek teeth in some 

 of the specimens is somewhat greater with respect to the orbit and 

 glenoid fossa than in E. grevyi skulls in comparable stages. The 

 distance between the incisors and cheek teeth varies appreciably but 

 averages somewhat less than in E. grevyi. Also the surface of occlu- 

 sion on the incisors appears on the average to be more nearly in line 

 with the occlusion of the cheek teeth. In Equus the position of the 

 occlusion of the incisors is generally somewhat lower. 



Indices or ratios of various measurements of the skulls, while 

 apparently significant in a series of recent skulls where accurate 

 measurements can be made, can not be determined satisfactorily or 

 even approximately in the Hagerman collection where based on 



