Geometrica-Group of S.A. Tortoises. i8i 



which narrow black bands are displayed. The following tints are 

 found to occur : Pale yellow or straw colour, lemon, light and dark 

 orange, reddish yellow, yellowish brown, and liver red. Usually 

 any one tint is characteristic of an individual, but occasionally the 

 distal part of the ray is darker than the part near the areola. The 

 colours are rarely very clear and bright on the natural shell, but 

 when the latter is wetted or rubbed with oil they are displayed in a 

 brilliant manner. 



Though the yellow rays present very varied appearances in the 

 different sub-groups, a general underlying plan can be traced through- 

 out,, and followed in its greater and greater elaboration through the 

 series. The simplest condition is that found in tentoria, and the 

 most complex in oculifera. In the former a number of simple yellow 

 bands radiate from the areola, which is also yellow ; some of the 

 rays extend all the way from the areola to the margin, while others 

 are shorter, due to incompletion either proximally or distally. The 

 width of the ray also varies much, and may be the same throughout 

 or increased distally ; frequently a broad ray is bifid distally. In 

 general, the rays of one shield show no correspondence in position 

 with those of the adjacent shields, so that no complex geometrical 

 pattern for the whole shell is possible. 



The neural and costal shields of tentoria are roughly quad- 

 rangular in their basal outline, and in some individuals there is a 

 tendency for the rays passing to the four angles of the shields to be 

 more conspicuous than those intermediate, and also for those of 

 adjacent shields to correspond, thereby giving a more definite geo- 

 metrical plan. All the types of the geometrica-gxovi-^ show this to be 

 the fundamental disposition of the rays on both the neural and costal 

 plates. The principal rays extend from the areola to the angles of the 

 shields, and these four are the most conspicuous rays; midway 

 between two adjacent principal rays may be another ray, and alter- 

 nating with these two series may be others of lesser rank. The 

 four principal rays will be spoken of as primary; the four inter- 

 mediate, one or more of which may be wanting, will be secondary 

 rays ; and the third series, not always present, will be tertiary rays. 

 On all the shields the four primary rays are always conspicuous, 

 and, in the more complex patterns, such as those of oculifera, they 

 are bifurcated distally. The secondary rays alternate with the prim- 

 ary, and vary much in the extent of their development ; rarely they 

 are all wanting on individual shields. Frequently the two longitudi- 

 nal secondary rays of one shield correspond with those of the two 

 adjacent shields, one in front and one behind, and thus give rise 

 to a continuous yellow band, which is median along the neural shields 

 and lateral along the costals on each side. The tertiary rays 

 are generally imperfectly developed, and are rarely numerous except 

 in certain tentoria. By the continuity of the two primary rays of 

 one shield with the two primary rays of an adjacent shield there is 

 produced a " diamond pattern " which, combined with a median 

 band, gives an ocellated character to the carapace. This is very well 

 shown in some specimens of the verreauxii sub-group (see Boulenger's 



