170 Transactions South African Pliilosopliical Society, [vol. xii. 



pressed, longer than the three following which decrease in size, and 

 often as long as the four joints. 



The males and females differ very much not only in the armature 

 of the head and prothorax, but also occasionally in the sculpturing 

 of the prothorax. Unless captured together it is very difficult often to 

 ascertain their identity. Not only does the development of the males 

 vary enormously, but it is well-nigh impossible to differentiate many 

 of them from normal females without dissection, and in the great 

 development the female itself assumes some of the male characters, 

 although on a reduced scale, and might well be taken for a male of 

 the intermediate or minor development. One distinctive character, 

 however, I find to be constant in the South African species : in the 

 female the fore tarsi which are inserted above the carina on the 

 lower face of the tibia, are always nearer to the inner angle of the 

 tibia than in the male, owing to this carina being more defiexed 

 at tip in the former than in the latter, but while this character is 

 constant, it is not always very conspicuous, principally when the 

 inner apical angle of the tibia is not spinose in the male ; but when 

 it is spinose, that of the female is always non-spinose. 



The shape of the apical spur of the fore legs varies much. It may 

 be : (1) nearly straight in both sexes, but always with a more pro- 

 nounced outward bend in the male : (2) equally bent inw^ardly at tip 

 in both sexes (0. i^yramidalis , i^anoplus) : (3) stouter and bent in- 

 wardly at tip in the male only (0. dispar, auriculatus, moestus) or 

 (4) stouter and bent inwardly at tip in the female and not in the 

 male (0. rams, ficrcifer, bi-callosns, briccci, aciculatus, &c.). 



In the last-mentioned group I find that the thickened and 

 sharply bent apical spur of the female is associated with a sub- 

 aculeate metasternum. The insects included in this group have, 

 however, a very different facies ; cf. 0. rants and 0. aciculatus. 



The head has either a transverse frontal carina, which in many 

 cases is either absorbed, or is rendered nearly obsolete by the great 

 development of the cephalic horn or horns when these spring from 

 the middle of the vertex, but which is very distinct in the inter- 

 mediate or minor developments in the male ; this carina may be 

 altogether absent in this sex, but I do not know as yet of this frontal 

 carina being absent in the female. I know of only two species in 

 which there is another carina above but parallel to the frontal one 

 (0. bouinus, inter stitialis). The shape of the prothorax varies very 

 much, but wherever the length of the horns is greater than usual, 

 the depth and width of the thoracic cavities is also greater, which 

 goes to show that the great size of the former has been obtained at 

 the expense of the latter. 



