Geometrica-Group of S.A. Tortoises. \gg 



which were secured much nearer the source of Smith's original 

 specimens than those from German South-West Africa. In all the 

 other details mentioned by Siebenrock there is nothing which is not 

 to be found among the Hanover specimens. If the coloration given 

 should prove to be a constant feature, it might mark a point of 

 departure of the Namaqualand specimens from the original type as 

 described by Smith. 



Verreauxii evidently extends across the middle northern part of 

 Cape Colony, probably all along both sides of the course of the 

 Orange River into German South-West Africa. Its area of distribu- 

 tion is thus between tentoria to the south and oculifera to the 

 north. 



Taken by themselves, individuals of verreauxii would certainly 

 be regarded as representing a distinct species of the geometrica- 

 group, but, when we see how strictly transitional in every character 

 are the more inland forms of tentoria, it is impossible to regard 

 verreauxii as but a variety of the older species. 



e. Testudo trimeni, Boulenger, 1886. 



The forms included by Boulenger under this term possess what 

 seem to be fairly fixed and constant characters, though decidedly 

 transitional. The species was founded upon a number of specimens 

 obtained by the Rev. G. H. R. Fisk from around the mouth of the 

 Orange River, Namaqualand, and in the South African Museum 

 are other specimens also collected by Mr. Fisk in this region. These 

 specimens agree in nearly every particular with Boulenger's 

 description and figures. 



The coloration of the carapace in trimeni can be easily derived 

 from that of tentoria or verreauxii, while that of the plastron, show- 

 ing the early stages in ray development from the continuous middle 

 black patch, is like that of some tentoria and geometrica ; the absence 

 or rudimentary nature of the femoral tubercle compares with other 

 coast forms. The yellow spot or streak at the junction of two costal 

 plates, considered to be of some diagnostic importance by Boulenger 

 and Siebenrock, is a very frequent character in verreauxii and 

 geometrica, and represents the rudiments of either secondary or 

 tertiary rays ; moreover, it is by no means a constant character in 

 trimeni, for in most of my specimens it is either wanting or repre- 

 sented by a continuous secondary ray- 

 Compared with those of other sub-groups, the characters of tri- 

 meni are of a very generalized nature, there being no instance among 

 them of extreme modification. They clearly exemplify how species 

 may originate by the cessation of variation, for although none of 

 the characters have reached the extremes they possess in oculifera, 

 they appear already fixed and stable. Were the transitional forms 

 to disappear, the combination of characters reached in trimeni would 

 be well worthy of specific recognition, but with the gradations towards 

 it from both tentoria and verreauxii, it cannot be regarded a distinct 

 species in a strictly logical sense. Geographically, it borders on 

 verreauxii and tentoria. 



