i8o Report S.A.A. Advancement of Science. 



subject of genetics, or even to strengthen and further illustrate 

 conclusions already accepted. Such studies naturally follow in the 

 train of the systematist. The systematist is the pioneer ; he discovers 

 and describes his species, he makes known what material is available, 

 and then the evolutionist attempts to show from a study of relation- 

 ships and environmental conditions how the different forms have 

 come to be, that is, their method of transformation. 



The object of the present paper is to discuss in a preliminary 

 manner the various characters which are relied upon by systematists 

 for diagnostic purposes vvithin the geometrica-group, to endeavour to 

 trace how the characters have been evolved, and how by their com- 

 binations they have given rise to types which are, or may ultimately 

 become, distinct species ; we have to consider, first, the variations of 

 the individual specific characters, and, second, the origin of the 

 specific types. With the acquisition of still further material, it is 

 hoped that a more complete account will be possible, illustrated by 

 coloured drawings. 



The claim for specific recognition of the ten forms hitherto 

 described will be discussed later. For present needs the following 

 may be allowed to be sufficiently well differentiated to warrant their 

 acceptance as distinct species or, perhaps better, as sub-groups, 

 namely : geometrica, ocidifera, tentoria, and trimeni. As regards 

 the other species described, it is, to my mind, very doubtful whether 

 they can be considered as representing more than one complex 

 assemblage, the members of which are as yet very fluctuating in 

 nearly all their characteristics. The evidence for this conclusion will 

 be presented later, and in the meantime I shall consider them as 

 grouped around verreauxii. 



The following are the principal faxonomic characters which are 

 relied upon for distinguishing the various specific forms : (a) Colora- 

 tion of carapace and plastron ; (b) axillary and inguinal shields ; (c) 

 margin of carapace ; (d) margino-costal angle ; (e) nuchal shield ; (f) 

 antebrachial shields ; (g) femoral tubercle ; (h) form of shields of 

 carapace and plastron ; (j) beak ; (k) frontal and prefrontal shields. 



I. I. INDIVIDUAL SPECIFIC CHARACTERS. 

 a. Coloration of Carapace. 



As already indicated, the coloration of the shell is the most 

 distinguishing and conspicuous character of the geometrica-group, 

 and, from its general similarity throughout, is the one feature which 

 at first sight suggests the close relationship of the different members 

 of the group. It consists essentially of a series of yellow rays on 

 a black or dark brown background. The rays on each shield radiate 

 all the way from the central areola to the margin of the plate, though 

 sometimes they extend only a part of the distance. 



The yellow rays vary much in number, width, length, arrange- 

 ment, and tint in different forms. Sometimes they are so broad that 

 the lighter colour may be regarded as constituting the background on 



