North American Centropagidce. 255 



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second segment of the right leg, which Schmeil ('98) says he 

 could not find, was present in all the specimens examined by 

 the writer. In one of the two specimens of females examined 

 the last segment of the fifth leg was armed with five spines, 

 as shown in the original figures, while the other had six. 

 I think that six may perhaps be found to be the rule, in 

 which case the species approaches nevadensis and laeustris 

 more closely, the former having six and sometimes seven 

 spines, and the latter constantly seven. The fact that none 

 of the other writers, Lilljeborg, de Guerne and Richard, and 

 Schmeil, have mentioned the existence of a sixth spine would, 

 however, militate against this assumption. 



The male of nordenskioldi is very easily distinguished from 

 the males of the other two species. The fifth pair of legs, 

 while of the same general type as in the rest of the genus, are 

 less modified and yet very characteristic. But for the fact 

 that it is, as a rule, difficult to make out, the hook-like process 

 on the first segment of the right leg would alone serve to 

 distinguish nordenskioldi. Further, the right leg is three- 

 segmented instead of two ; the last segment is armed on the 

 outer margin, at the apex, with a small spine ; and the hook 

 on the first segment of the left leg is comparatively simple.' 

 The abdomen is also less modified than that of nevadensis 

 and laeustris. Instead of being quite strongly flexed to the 

 right it is almost or entirely straight, while the processes are 

 small and inconspicuous, there being some difficulty in dis- 

 cerning the one on the fifth segment. 



The fifth pair of legs of the female also serve, though not 

 so readily, to distinguish this species. They differ from those 

 of laeustris in that the last segment is armed with only five or 

 six spines, instead of seven, and in the relative length of the 

 segments. From the fifth legs of nevadensis they may be 

 distinguished by the difference in proportions, those of neva- 

 densis being much more robust than those of nordenskioldi, 

 which are intermediate between the other two. The different 

 arrangement of the spines on the last segment, the occasional 

 absence of the sixth spine on this segment, and the presence, 

 at least occasionally, of a second spine at the outer apical 



