15— VARIATIONS IN THE GEOMETRICA-GROUP OF 

 SOUTH AFRICAN TORTOISES. 



By J. E. DuERDEN, Ph.D., A.R.C.S. 



Professor of Zoology, Rhodes University College ; Keeper of 

 Zoological Department, Albany Museum. 



2. Discussion. 



a. Type of Variation. 



b. Fixity and Plasticity of Characters. 



c. Introduction of New Characters. 



II. I. Specific Types. 



a. Testudo geometrica. 



b. Testudo oculifera. 



c. Testudo tentoria. 



d. Testudo verreauxii. 



e. Testudo trimeni. 

 /. Testudo smithii. 

 g. Testudo fiskii. 



h. Testudo strauchi. 

 i. Testudo seimundi. 

 j. Testudo boettgeri. 



2. Discussion. 



a. Number of Species represented. 



b. Geographical Distribution. 



c. Original Type of the Geomeirica-group. 



III. Summary. 



INTRODUCTION. 



In South Africa there occurs an extremely well-defined group 

 of tortoises, all the species of which are referred to by Prof. G. A. 

 Boulenger, in the British Museum Catalogue of Chelonians, as 

 " allied to Testudo geometrica.'' They are readily distinguished 

 from other tortoises by having a black or dark brown carapace, each 

 shield of which is conical with bright yellow rays extending from 



