G. O. Sars. 



Description of the female. 



The length of the body in the largest specimens ex- 

 amined, not including the caudal setæ, amounts to about 

 5 mm., and this form accordingly grows to a very large 

 size, and is in this respect almost unrivaled by any other 

 known fresh-water species. 



The form of the body (see figs. 1 and 2 of the accom- 

 panying plate) is comparatively rather robust, and, on the 

 whole, resembles that in the larger species of Diaptomus. 

 The anterior division is very sharply marked off from the 

 posterior, and oblong subcylindrical in form, being about .3 

 times as long as it is broad. As in Diaptomus, it is, com- 

 posed of 6 well-defined segments, the anterior of which, 

 representing the head, is much the largest, attaining almost 

 the length of the 3 succeeding segments combined. This 

 segment, which below carries the antennæ and oral parts, 

 is of about the same width in its posterior part as the suc- 

 ceeding segments; but anteriorly it gradually tapers, so that 

 the front, seen dorsally (see fig. 1), appears narrowly rounded, 

 about the middle, this segment has a well-marked dorsal 

 depression, the cervical sulcus, best seen in the lateral view 

 of the animal (fig. 2). The front terminates in an obtuse» 

 somewhat deflexed prominence, which is without tentacular 

 filaments. The lateral edges of this segment form a well- 

 marked, somewhat wavy line on each side, passing from the 

 front backwards, just above the insertion of the several 

 appendages (see fig. 2). By these lines a rather narrow 

 ventral area is defined, which, in the region of the mandibles, 

 projects to the anterior and posterior lips, between which 

 occurs the oral aperture. 



