i88 Report S.A.A. Advancement of Science. 



where the central shields have disappeared, with the exception of 

 one which is much enlarged, thickened, and excentrically conical. 



Transitional stages towards the variation in geometrica are not 

 represented in the collections, but no doubt such would be found in a 

 larger series of specimens from the Western Province of Cape 

 Colony. As compared with tentoria, there has been a reduction 

 in the number of prominent scales without any tendency for one to 

 become larger than the others. Five or six enlarged shields occur, 

 but are so far apart as not to be imbricating. It clearly represents a 

 different type of modification from that culminating in oculifera. 



Test/ido trimcni represents another slightlv different type in the 

 arrangement and character of the arm shields, but one towards which 

 there are numerous intermediate stages. In the most characteristic 

 specimens are four specially enlarged, flattened shields, arranged 

 in a continuous median row from the elbow to the fingers, and along 

 the two sides of this row are a series of scales moderately enlarged. 

 It is found, however, on comparing the shields of a number of speci- 

 mens of trimeni with those of tentoria and verreanxii, that all inter- 

 mediate varieties from one extreme to the other can be traced. 



Therefore as regards the enlarged antebrachial shields at least 

 four more or less well-defined types of variation are represented in the 

 geometric a-gvoup : i, the numerous, elongated, imbricating shields 

 of most tentoria; 2, the few scattered, non-imbricating shields of 

 geometrica ; 3, the single row of four flattened shields in trimeni; 

 4, the single, greatly enlarged, thickened, sub-conical shield of 

 oculifera. Between these extreme types, with perhaps the exception of 

 geometrica, all intermediate or transitional stages are still to be 

 obtained. With all these facts before one, there can be no question 

 that the extremes represent so many lines of variations or departures 

 from a common source. 



//. Femoral Tubercle. 



The femoral tubercle is a greatlv enlarged, conical shield, situ- 

 ated upon the back region of the thigh, which, when the animal is 

 retracted, assists in the protection of the vulnerable parts at the 

 hinder opening of the shell. The tubercle may be single on each side, 

 but is frequently surrounded by others of much smaller size, inclined 

 against it after the manner of buttresses ; occasionally on each side 

 are two tubercles of equal size, or one may be larger than the other. 

 In addition to the strictlv femoral tubercle a number of enlarged 

 shields sometimes occur, arranged in longitudinal rows along the 

 sides and over the upper surface of the short tail, and without doubt 

 also serve to protect this region. 



The femoral tubercle is developed to very different degrees in 

 the various assembla-^es of the geofnetrica-gvoup. Boulenger, in his 

 British INIuseum Catalogue, employs the character as a means of 

 separating geometrica, verrcaitxii, and trimeni from the rest; the 

 three mentioned are stated to have no enlarged femoral tubercle, 

 while such is present in the others. As regards geometrica. the 



