132 Annals of the South African Museum. 



ing the specific name. I have already pointed out in a previous 

 paper (p. 1 of this volume) that the sexes maybe readily distinguished 

 by the structure of the operculum, a character which holds good for 

 even fairly young specimens and is the only perfectly reliable 

 one. 



The structure of the pectines invariably differs with the sex. In 

 the female the scape is always free of teeth for a certain distance at 

 the base behind, while in the male it is either toothed along the 

 whole length of the hind margin or it is also without teeth at the 

 base; in the latter case, however, this toothless portion always 

 represents a smaller proportion of the whole length than in the 

 female of the same species. The limit to the number of teeth is also 

 always highest in the male and lowest in the female. Pectinal 

 characters do not alter with age. 



As regards other characters, the two sexes are very much alike up 

 to the time when the last moult takes place ; in the nearly full-grown 

 males, however, some of the characteristic granulation of the adult 

 may appear, while the hand is generally a little narrower than in the 

 female of the corresponding stage. In these pre-adult stages the 

 hands are often much darker in colour and more granular than in 

 the adults in both sexes. 



In the adult female the hands are wider in proportion to the 

 length of the hand back than is the case in the previous stage ; but 

 it must be remembered that in adult specimens from one locality 

 this proportion may be the same as that found in nearly adult 

 specimens from another locality (e.g., in wahlbergi). The adult male 

 is generally easily recognisable by the characteristic form of the 

 hands and tail. After the last moult the hands appear narrower, 

 natter, and often longer and smoother than in the female, while the 

 tail becomes much longer and nearly always stouter. Generally the 

 first and second caudal segments together equal the carapace in 

 length (in the female the length of carapace generally much exceeds 

 that of the first two caudal segments). In the adult male the terga, 

 sterna, and under side of the anterior caudal segments are often 

 much more granular and the palps much longer than in the female or 

 young males, while the anterior upper crest of the humerus is 

 undeveloped in the females of some species. 



Specific Characters. As the species of this genus are both 

 numerous and very variable, I have thought it advisable to 

 discuss the relative value of the characters available for classifica- 

 tion. 



1. The presence of a well-developed, Y-shaped, forked groove on 



