Tllli DISTRIBUTION AND CHAR.\CTEKS OF KEI'TILES. 24I 



distinguished as they are by profound differences of climate. 

 A number of widely distributed tropical species reach as far 

 south as Natal or Eastern Cape Colony, but are quite unrepre- 

 sented in the Western parts of the Cape, probably because the 

 climate is unsuitable, cf., the lizards Homopholis zvahlbergi, 

 Lygodact\'lus capeiisis, Mabuia quinquetaeniata, and the snake 

 Dendraspu angusticeps : in many other cases a widely distri- 

 buted tropical species reaches as far south as Natal or Eastern 

 Cape Colony, but in Western Cape Colony is represented by a 

 closely allied species. The water frog, Rana angolensis. occurs 

 from Angola to German East Africa, and passes southwards 

 along the Southern coast as far as George, but in the Karroo and 

 Western districts of the Cape it is replaced by R. fuscigula, a 

 closely related form : the cobras Naia haie and N. mgricollis 

 extend from the Nile to Natal, but in the Cape are replaced by N. 

 flava : the toad Breviccps mossamhicus ranges from German East 

 Africa to Natal, but our Cape form is gibbosiis : the common toad, 

 Bufo regularis occurs practically throughout Africa except Bar- 

 bary, but is unknown in the carroid regions of the Cape, where, 

 however, B. garicpensis (granti) is common. Now, as there is no 

 strongly defined geographical barrier separating the Eastern and 

 Western parts, there is great probability that the differentiation 

 of species in these cases has been determined by climate and 

 related environmental influences. 



Amongst all genera of Lizards in South Africa, it is the 

 general rule that closely related species of the same genus are 

 geographically separated, and not only so, but usually in such a 

 way that the specific areas coincide with regions of very different 

 climatic or vegetational condidions : on the other hand, the Ameri- 

 can systematists in various groups of animals report that their 

 closely allied species occupy distinct portions of the same environ- 

 mental area, this being broken up by natural barriers which pre- 

 vent free communication. 



The hispida section of the genus Agama is distributed some- 

 what on the same plan as the species of Zonurus. A. hispida 

 proper, seems to be confined to the South-West parts of the 

 Cape. A. brachyiira occurs in Little Namaqualand, and other 

 Western parts of the Cape, A. distanti occurs on the high veld of 

 the Free State and Transvaal, A. aculeata occurs in the Kalahari, 

 Namaqualand and the Karroo, whilst A. armata ranges from 

 Natal to East Africa. Unlike Zonurus, hoewver, these species 

 are neither greatly nor sharply separated from each other in their 

 structural characters. We may add that A. atra, which struc- 

 turally belongs to a different section of the genus, occurs in tlie 

 same localities as any of the above-mentioned species, though it is 

 actually quite isolated topographically from any Agama that may 

 live in dts neighbourhood, owing to its rock-frequenting habits. 



The distribution of the geometric tortoises has much in 



