10 Gt. 0. Sårs. [No. 4 



besides the usual natatory seta, each of the 2 first joints has a well- 

 defined setiform spine outside, and the 3rd joint has 2 similar spines 

 and 5 natatory setæ, 2 of which issue from the tip. The inner 

 ramus has the proximal joint somewhat shorter than the distal one, 

 and is provided with only a single natatory seta inside. The distal 

 joint carries 6 such setæ, 2 on the inner edge, 1 on the outer, and 

 3 on the tip. 



In the 3 succeeding pairs (figs. 4, 6) the out er ramus has no 

 true spines outside; but each of the joints is only produced at the 

 end to a short dentiform projection. The terminal joint carries on 

 the tip a very long and slender, sword-shaped spine, bordered out- 

 side with a thin, coarsely-serrate rim (see fig. 5), and has, more- 

 over, 5 slender natatory setæ, all originating from the inner edge. 

 On the inner ramus, the proximal joint is much longer than the 

 distal one, and carries in the 2nd and 3rd pairs (fig. 4) 2, in the 

 4th pair (fig. 6) 3, comparatively short setæ. The number of setæ 

 on the terminal joint of this ramus in the 2nd and 3rd pairs is 7, 

 in the 4th pair 6. 



The last pair of legs (fig. 7) are very different from the pre- 

 ceding pairs, and are not natatory. As compared with those in Acartia, 

 they are much more strongly built, and moreover differ in the com- 

 plete fusion of the basal parts, their original duplex nature being only 

 indicated by a slight incision behind. On each side of this common 

 basal part, a delicate ciliated seta is attached. The terminal part 

 of each leg has the form of a very strong curved claw, slightly 

 dilated at the base and armed on both edges with coarse denticles. 

 On a closer examination, the right claw is constantly found to be 

 somewhat larger than the left. 



Deseription of the Male. 



(PL IV). 



The adult male is of nearly the same size as the female, but is 

 of a very different external appearance. Seen dorsally (fig. 1), the 

 anterior division of the body exhibits a rather regular narrow fusiform 

 shape, with the greatest width about in the middle, and gradually 



