NO. 2212. 



A NEW SPECIES OF EXTINCT HORSE— HAY. 



437 



In Nehring's eight small horses the cranio-cephalic index ( = 

 cranial length X 100 -^ basilar length) averaged 36; in the eight 

 large horses it averaged only 33. In the Yukon skull it is 35.7. 



In the eight small horses of the tables referred to the f acio-cephalic 

 index (facial length X 100 -^basilar length) average 76.1; in the 

 large horses, 74.1 In E. lamhei it is 76.9. 



It is seen therefore that as compared with the races of Equus 

 cdballus the Yukon species, E. lamhei ranges itself with the small 

 horse having short and broad heads, but with a high facio-cephalic 

 index. 



It will be well to compare certain indices of the species here de- 

 scribed with those of four other forms. 



Table of indices. 



Species (types.) 



Equus niobrarensis 



E. niob. alaskae 



E. hatcheri 



E. laurentius 



E. lambei 



Cephalic 

 index. 



45.2 



44.2 



42.8 



43 



44.4 



Facio- I Cranio- 

 cephalic cephalic 

 index. index. 



Index of 

 tooth line. 



It will be observed that the Yukon horse stands above the others 

 of the table in the facio-cephalic and the cranio-cephalic indices and 

 the index of the tooth line. 



It is found that the brain case of the Yukon horse exceeds in size 

 that of two skulls of the domestic horse at hand. In one of these, 

 No. 843 of the United States National Museum, the width of the 

 brain case is 21.1 per cent of the basilar length; the height above 

 the lower surface of the cranial axis, 19.1 per cent. In the other, 

 an old horse, No. 5044, the percentages are respectively 20.6 and 19.3. 

 In the Yukon horse the percentages are both 23.1. 



The lower jaw (pi. 56, fig. 1) differs greatly from that of an old 

 domestic horse at hand. In the latter the angle of the jaw is very 

 broad, and the width at the last premolar is only a little more than 

 half that at the angle. In the Yukon horse the greatest width is 

 112 mm.; that at the last premolar, 84 mm.; just .75 of the width at 

 the angle. This angle is very broad in E. laurentius.- The lower 

 jaw of E. niobrarensis^ and that of E. katcheri* resemble consid- 

 erably that of the species here described. 



^ These indices are taken partly from a table on page 590 of volume 44 of the Pro- 

 ceedings of the U. S. National Museum. Through an error the abbreviation mm. Is 

 found at the head of each of the columns of that table. 



' Proc. U. S. Nat. Mus., vol. 44, 1913, p. 72. 



•Idem, pi. 70. 



*Proc. U. S. Nat. Mus., vol. 48, 1915, pi. 32. 



