108 ORTMANN — AFFINITIES OF CAMBARUS. [April i 3 , 



(digueti-group) , and that the development of an additional pair of 

 hooks on the fourth pereiopods is a parallelism to the similar ten- 

 dency in the more highly advanced forms of the subgenus Cambarus 

 {blandingi group) : to the latter, C. pellucidus has no direct relation 

 at all. 



With regard to all the rest of the species of this subgenus, I 

 agree with Faxon in thinking them to form a natural, genetically 

 connected group. Nevertheless there is much diversity within 

 this subgenus, and is chiefly indicated by the shape of the male 

 sexual organs. Faxon did not use the latter in arranging the 

 species of his fourth group, and thus his key (1885, p. 86) is, as 

 he admits himself, artificial to a degree. But I shall show here, 

 that according to the sexual organs we can divide the subgenus in 

 groups, which seem to be quite natural. 



1 . Section : C. limosus. 



Sexual organs short, rather thick up to near the tips, reaching to 

 the base of the third pair of pereiopods. Tips split for a short 

 distance, each tapering to a point. Hooks on third, or on third and 

 fourth pereiopods. 



This is the most primitive section of the subgenus, and it is also 

 in other characters quite indifferent, and not highly specialized ; 

 and further, it appears a little heterogeneous. The rostrum is 

 quite uniform in shape, generally with marginal spines (except in 

 certain varieties of C. pellucidus) , with a rather long or a moderate 

 acumen. The areola is wide and of medium length (except C. 

 pellucidus) ; the chelae are comparatively narrow and without 

 remarkable features (except in C. harrisoui). 



The annulus of the female shows the tendency to develop tuber- 

 cles upon its face ; these tubercles have a more or less central 

 position (limosus, indianensis), or a posterior (sloanei), or have 

 the shape of a transverse ridge (harrisoni), or form a "median 

 keel" (pellucidus). 



2. Section : C. propinquus. 



Sexual organs shorter or longer, not thick, deeply split at the tips, 

 tips slender, more or less straight, sometimes the onto- one slightly 

 curved, but never both tips curved in the same direction. Always 

 only third pereiopods 7vith hooks (barring freaks) . 



The other characters are very uniform in this section. The 

 rostrum possesses with one exception ( C. tnedius), marginal spines, 



