COMMON ZEBRA OR BONTE-QUAGGA 675 



tsetse-fly diseases so prevalent among the big game of 

 Africa to-day and not to any change in the cHmate, flora, 

 or balance of large carnivorous animals which preyed upon 

 them. 



Key to the Genera of Equidce 



Head not enlarged; skull wider, the snout or rostral portion not greatly 

 lengthened; occipital portion of skull not produced 

 backward beyond the condyles; lambdoidal crests 

 narrow; coloration when striped having the dark 

 stripes much wider than the light ones and the hind 

 quarters crossed by diagonal or longitudinal stripes 



Equus 



Head somewhat enlarged and elongate or dolichocephalic; skull nar- 

 rower, the rostral portion lengthened and the occip- 

 ital or lambdoidal crests very wide and extending 

 well behind the condyles; dark and light stripes 

 numerous and equal in width over most of the body; 

 rump crossed by transverse stripes to below the hips 



Dolichohippus 



Horses, Asses, and Zebras 

 Equus 



Equus Linnaeus, 1758, Systema Naturae, p. 73; type E. caballus, the domestic 

 horse. 



The modern representatives of the genus Equus show 

 great range of coloration from the fully striped zebras 

 through the partially striped asses to the unicolored horse. 

 In body shape or in actual size there is comparatively little 

 range if we exclude the giant domestic breeds of horses 

 which have no standing in nature. The ears range from 

 the great length found in some asses to the short, narrow ear 

 of the horse and bonte-quagga. There is a progressive de- 

 velopment in the size of the tail tuft from the small terminal 

 tuft of the zebra to the complete tufted tail of the horse. 

 The skulls, however, show surprisingly slight differences in 

 shape or dentition and are scarcely distinguishable. The 

 horse is more distinct than the other species and may be 

 distinguished by its larger cheek-teeth in which the inner 



