Geometrica-Group of S.A. Tortoises. 185 



from four or five to only one, and in an extreme case, where only one 

 is present, it seems to have lost its individuality and become a part 

 of the adjacent humeral shield. The fluctuating character at the inter- 

 mediate stage is well shown in individuals of verreauxii, where the 

 number may vary from one to three, and even differ on the two 

 sides of the same individual ; the number is a very fixed character in 

 oculifera and geometrica, where in numerous specimens there is no 

 hint of more than one. 



The inguinal shield represents all that remains of the posterior 

 inframarginals and is nearly always single, but in some individuals of 

 ientoria, verreauxii, and trimeni one or two small additional shields 

 are present. The additional shields vary in their degree of develop- 

 ment in individuals of the same sub-group, and often on one 

 side of a specimen as compared with the other, proving the character 

 to be very fluctuating. 



d. Margin of Carapace. 



The free edge of the carapace differs much in appearance in 

 the various members of the geometrica-gvouY). In some it is quite 

 smooth and rounded, while in others the individual marginal scales 

 are sharply angulated, when the margin is described as serrated. 

 Tentoria may be taken as the extreme representative of the first type 

 and oculifera of the second. As in other characters, all intermediate 

 stages occur between these extremes. Not only tentoria, but also 

 trimeni and geo?7ietrica present an almost unbroken margin, both 

 anteriorly and posteriorly ; occasionally, however, there is a feeble 

 serration, more marked along the hinder border. The carapace of the 

 verreauxii sub-group is found to be very variable ; both the anterior 

 and posterior borders are nearly always serrated and upturned, but 

 the degree to which the modifications are carried differs greatly. In 

 oculifera the serrated upturned condition is always strongly pro- 

 nounced, both in front and behind, and imparts a decided spinous 

 character to the shell. 



To summarise : the upturned serration is to be regarded as a 

 fixed permanent character in oculifera; the almost smooth, rounded 

 margin occurs in tentoria, trimeni, and geometrica ; verreauxii is 

 undoubtedly transitional between the two, some individuals approach 

 tentoria and others oculifera. 



Frequently there occurs an irregular longitudinal shallow groov- 

 ing towards the lower edge of the marginal plates, most conspicuous 

 in the median shields united with the bridge. It is pronounced in 

 some members of the tentoria, trimeni, and verreauxii groups, but has 

 little diagnostic value. 



e. Margino-Costal Angle. 



In several of the geometrica sub-groups there is a strongly 

 marked longitudinal depression or groove which separates the mar- 

 ginal series of shields from the adjacent costals. The groove extends 



