240 



THE DISTRIBUTION AND CHARACTERS OF REPTILES. 



species last mentioned as due to peculiar environmental condi- 

 tions when the wide range of cordylus is considered, and as 

 their scutellation characters are in some respects primitive they 

 are, perhaps, best regarded as isolated sections of the original 

 variable stock. However, if this case may be thus explained, 

 it is the only example known to me of differentiation of species 

 solely as a result of geographical isolation within a uniform 

 environment. Excepting the case of Z. cordylus and its two 

 nearest allies, vittifer and jonesii, the genus Zonurus is remark- 

 able amongst lizards in South Africa in that species whose areas 

 are geographically adjacent are apparently not closely related: 

 for instance, cordylus, the coastal si)ecies of the Cape, gives 

 place to cataphractns in Little Naniaqualand, to polyzonus in 

 the central and northern regions of the Cape, and this, again, is 

 succeeded by gigantcits in the Free State, but these four species 



±t MACR0PH0LI5 {.no^ precisely t 

 ^^ locahed) 



ri:;;; coerulcopunctatos 



CATAPHRACTUS 



■ WARRENI ^^_ 



ACAPEN3I5 



Distribution of tht species of Zonurus in South Africa. 



are very sharply separated from each other in a number of 

 their specific characters. It is probable that these large 

 differences between the species are in part a result of their 

 sluggish and retiring habits, which facilitate geographical 

 isolation. 



Sluggishness of habit certainly favours the differentiation of 

 a genus into species. The pumilus group of chamaeleons, 

 which are proverbially slow of movement, coinprises half a 

 dozen or more species, each of which is the local form of some 

 area along the southern coast : but how far the differences are 

 due to isolation, and how far to environmental differences, it is 

 hard to say, as it cannot be said that the environmental condi- 

 tions are identical in any two cases. No other genus of lizards 

 is split up into so many species within the same region. 



It is interesting to note the change of fauna in passing 

 from the Eastern to the Western districts of South Africa, 



