398 University of California Publications in Geology [Vol. 7 



the skeleton. These collections, together with several skulls and 

 much scattered material already available, offer one of the 

 fullest opportunities for study of American Pleistocene horses 

 that has been presented. Satisfactory preparation and exami- 

 nation of the entire series of specimens will require many months' 

 work. In advance of this study it is possible to give such a 

 statement of the most important contributions made by this 

 collection as will assist in the interpretation of other material. 



The collection available contains eleven good skulls, several 

 imperfect specimens, and much fragmentary material. It repre- 

 sents animals of both sexes, and of all ages from foals with 

 unworn milk teeth to old individuals with dentition in advanced 

 stages of wear. The specimens show considerable variation in 

 the characteristics upon which our classification of American 

 Pleistocene horses has of necessity been largely based, and an 

 estimation of the significance of this variation will presumably 

 assist to some extent in interpretation of a number of the numer- 

 ous imperfectly known equine species described from the Amer- 

 ican Pleistocene. 



Up to the present time the only descriptions of satisfactory 

 skull material representing American Pleistocene horses are 

 those of Gidley 1 on Equus scotti of the Texas Pleistocene, and 

 Hay 2 on Equus niobrarensis and Equus laurentius from Nebraska 

 and Kansas. Of Equus scotti several skulls representing indi- 

 viduals ranging from youth to maturity are available. Skeletal 

 material accompanying the skulls gives to this species a full and 

 satisfactory representation. Of Equus laurentius the single good 

 skull known shows this form, with its slender skull and small 

 teeth, to be distinctly separated from the heavy-headed E. scotti 

 and E. niobrarensis. Of Equus niobrarensis an imperfect skull 

 from Hay Springs, Nebraska, shows most of the characteristics 

 satisfactorily excepting the frontal and facial regions. Another 

 specimen from the Pleistocene of Tofty, Alaska, is referred to 

 a subspecies, Ecjuus niobrarensis alaskae by Hay. The lower 

 jaws of this form were not found. The cranium lacks only 



1 Gidley, J. W., Bull. Am. Mus. Nat. Hist., vol. 13, pp. Ill to 116, 1900. 



2 Hay, O. P., Proe. U. S. Nat. Mus., vol. 44, pp. 576 to 591, 1913; and 

 Smithsonian Misc. Coll., vol. 61, no. 2, 1913. 



