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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 6l 



conal, valleys of the teeth of the Liakhof skull are not so wide as those 

 of the Alaskan skull and do not extend nearly so far toward the 

 center of the tooth. The little bay entering the tooth behind the 

 hinder inner pillar (hypocone) is much narrower in the Liakhof 

 horse than in the Alaskan. Likewise the bay entering the tooth in 

 front of the protocone is narrower, and the anterior end of the 

 protocone extends further forward inside of it. 



Tscherski attached much importance to the feature just mentioned, 

 the elongation of the anterior end of the protocone, and proposed an 

 index to express this. He measured the distance from the hinder 

 border of the tooth to the anterior border of the protocone and 

 divided this, multiplied by 100, by the distance from the hinder border 

 of the tooth to the nearest point of the anterior bay. His results on 

 the teeth of the Liakhof skull are given below, and with them the 

 indices derived from the skull forming the type of Equus niobrarcn- 

 sis, the Alaskan skull here described, two skulls of Equus grevyi, and 

 two of Equus burchelli granti. In each case the present writer has 

 taken the measurements from the hinder end of the under inner 

 pillar (hypocone). 



It will be seen from this table that the indices of the Liakhof skull 

 stand above all the others here measured. It will be observed also 

 that there is a considerable range in the cases of the two specimens of 

 Grevy's zebra and in the two of Grant's zebra. Inasmuch as both 

 the depth of the anterior bay and the extension forward of the 

 protocone may vary independently of each other, it would probably 

 be better to compare each with the length of the grinding surface or 

 with its width. 



While it must be admitted that the Liakhof skull resembles greatly 

 that from Alaska, the writer is not prepared to say that they belong 

 to the same species. It must be stated here also that, while Tscherski 

 in his work calls the Liakhof horse Equus caballus, he (p. 341) 

 expresses the opinion that in case the peculiarities of the skull should 

 be found repeated in other specimens, this might justify the specific 

 independence of the animal. 



