Geometric A- Group of S.A. Tortoises. 205 



Geometrica is the form found in the extreme south-western part 

 of Cape Colony, in the Cape and Malmesbury Districts. Its 

 extension requires further investigation, but cannot be very wide. 



Trimeni is found along the coasts to the north of geometrica, 

 along each side of the mouth of the Orange River, that is, in 

 Namaqualand and German South-West Africa. 



V erreaiixii has a very wide inland distribution, extending almost 

 across the southern part of South Africa, from Basutoland on the 

 east to German South-West Africa on the west. Within this area 

 have been obtained smithii, fiskii, seimundi, and boettgeri. 



Ocidifera occurs to the north of the zone of verreauxii, having 

 been obtained from Barkly West, Griqualand, Bechuanaland, and 

 Damaraland. 



Thus each well-defined type of the geometrica-^ro\x^ occupies a 

 very distinct geographical area in South Africa, the elevation and 

 other physiographic conditions of which vary considerably. If one 

 were able to study the peculiarities of the environment closely there 

 is little question that the variations would be found to be largely 

 adaptive, but the study of this aspect of the subject has not yet 

 been possible. Even if the adaptive nature of the variations were 

 established, it would not follow that the variations have been made 

 by the environment ; there seems much more evidence for the view 

 that the transformations are primarily a manifestation of qualities 

 inherent in the constitution of the organisms themselves — endonomic 

 selection. 



In a short paper on the South African tortoises of the genus 

 Homofns (Records of the Albany Museum, Vol. I., p. 410), I have 

 shown that the six species of this genus have likewise a very restricted 

 distribution, coinciding in some ways with that of the members of 

 the geometrica-^xG\y^. 



In contrast with the restricted distribution of the representatives 

 of these two groups is the wide extent covered by two other species 

 of South African tortoises, Testudo fardalis and Test7ido angulata. 

 In their general appearance these two are very different from one 

 another, and also from the species of Homofus and the allies of 

 T. geometrica. Any common origin must be far removed. Both 

 species are plentiful, and apparently extend all over South Africa. 

 Pardalis reaches to East Central Africa, and, along with angtdata, 

 is found in Natal ; no local variations of any importance have been 

 observed. It is very significant of the constitutional differences 

 among organisms when one reflects that these two forms are to be 

 found all over South Africa, without any important variations, while 

 species of Homofus and the geometrica allies are highly distinctive 

 of special divisions of this area. Evidently the members of the 

 Homofus and geometric a-^rc,v\-^% have been, and probably still are, 

 in a more variable or plastic state than fardalis and angulata; the 

 first two groups are in process of transformation under South 

 African conditions, while the others seem fixed. Of the two, 

 Homofus is at present much less variable than the geometrica series, 

 as no intergrading forms among its recognized species have yet been 

 found. 



