304 Mr. R. I. Pocock on the Equidse. 



Mr. Byrne, who lias seen Zeus alive at Plymouth, in- 

 forms me that it does not live well in an aquarium and has 

 not been observed to " sleep," but that it swims in a lop-sided 

 fashion, at any rate in captivity, and also seems to use the 

 soft dorsal and anal fins as organs of propulsion, moving 

 them in waves, much as a needle-fish does. 



XLTII. — A neto Arrangement of the existing Species of Fiqu'idae, 

 ivith the Description of a new Subspecies of " Zebras By 



K. I. Pocock. 



It is customary to classify existing Equidse as Horses, Asses, 

 and Zebras. 



The genus Equus, Linn. (Syst. Nat. ed. x. 1706)^ originally 

 contained E. cahallus (the domestic horse), E. asinus (the 

 domestic ass), and E. zebra (the mountain zebra, with whicli 

 Linnfens included the quagga). 



In 1825 Gray (Zool. Journ. i. p. 241) established tlie 

 genus Asinus for E. vulgaris { = asinus), E. zebra, E. (J'logfja, 

 and E. Burchelli. In other words, he divided the Kquidaj 

 into '' Horses " and " Asses." 



Hamilton Smith went a step further, and removed from 

 Gray's genus Asinus, under the name Jlippotiyris, IJ. zebra , 

 H. qiiagga, 11. Burchelli, and added H. antiquorum, leaving 

 Asinus tor the African and Asiatic species of wild ass 

 (Nat. Libr., Mamm. i. pp. 350-351). This classification 

 expresses in technical language the prevalent notion as to the 

 affinities of the species included, although generic value has 

 been seldom accorded to the three group?. It was adopted 

 nevertheless by Trouessart in 1898 (Cat. Mamm. ii.), 

 E. Grevyi and a number of subspecific forms of E. Burchelli 

 being included under Hippoligris. 



Zebra is no doubt a convenient vernacular term for the 

 striped as opposed to the unstriped species of Equidas ; but 

 its technical equivalent IJippotigris, in the broad sense used 

 b}' Hamilton Smith and tlie still broader application given 

 to it by Trouessart, cannot, I think, be maintained as 

 s} mbolizing a natural unit. 



T here is a mass of evidence favouring the view that the 

 ancestors of Equus were striped. In that case the stripes 

 of "zebras" are a heritage from a common ancestor. To 

 that extent only are they a sign of affinity between the species 

 which possess them. They have been retained where the 

 physical conditions required their retention lor purposes of 



