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 climate, 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 
