NO. 2 EXTINCT HORSE FROM ALASKA — HAY 7 



The greatest range in the size of the palato-cranial angle is seen 

 in the four skulls of Grant's zebra ; and the greatest difference is 

 seen to exist between No. 161930 and No. 161932. These two animals 

 were mature, but not aged, of nearly the same age, both males, and 

 both secured on the same farm in British East Africa. One has an 

 angle of 6.5 ° ; the other an angle of 20 . It will be observed that this 

 angle is relatively small in the type of Eauus niobrarensis and in the 

 skull from Alaska ; but other skulls of the species might furnish quite 

 different results. 



The gelding and the Arabian agree in having the occiput-vertex 

 angle equal to 77.5 ° ; the type of Equus niobrarensis and the Alaskan 

 skull agree in having it equal to 73.5 . 



The grinding teeth of the Alaskan specimen (pi. 1, fig. 2) resemble 

 greatly those of the type of Equus niobrarensis. The table above 

 given shows that those of the two skulls differ little in size. The 

 outer styles are equally prominent in the teeth of both. In both 

 skulls the protocone of the last premolar is longer than the protocones 

 of the molars. In the two hinder premolars of both skulls, the post- 

 protoconal valley is broad, has a deep re-entering loop in front, and 

 sends a long branch to the center of the grinding surface. In both 

 skulls these peculiarities of this valley are not so prominent in the 

 molars as in the premolars, and slightly less so in the molars of the 

 Alaskan skull than in the molars of the type. As regards the enamel 

 surrounding the cement lakes, there appear to be no important differ- 

 ences. In the type skull the hinder border of the hinder lake in the 

 first and second molars has a rather deep notch, while in the Alaskan 

 skull this is absent or extremely small. 



The incisors of the Alaskan skull (pi. 1, fig. 3) are in a slightly 

 more advanced stage of wear than are those of the type skull. All 

 have deep cups, that of the second incisor being 30 mm. deep. This 

 incisor, evidently, had the hinder wall notched, as shown by a sharp 

 groove in the rear of the tooth. The third incisor is worn down just 

 to the bottom of the notch. 



The width of the posterior nares, in front of the hamular processes, 

 is 46 mm. In the type of Equus niobrarensis the width is 46 mm. ; 

 in the Arabian horse, 50 mm. ; in the gelding, 60 mm. In the Alaskan 

 skull the width across the occipital condyles is 80 mm. ; in the type of 

 Equus niobrarensis, 84 mm. ; in the Arabian horse, 90 mm. ; in the 

 gelding, 99 mm. 



The Alaskan skull differs from all the others here mentioned in the 

 condition of the sagittal crest (pi. 2, fig. 1). The ridges which run 



