46 



penultimate trunk-segment conspicuously produced, each terminating in a sharp, 

 somewhat extant point. Last trunk-segment likewise acutely produc d laterally. 

 Genital segment longer than it is broad at the base, anterior part slightly dilated, 

 posterior sub-cylindrical in shape. Caudal rami comparatively shorter and less 

 narrow than in C. lucidulus, not attaining the length of the last 3 segments 

 combined, and scarcely divergent ; seta of outer edge rather coarse and somewhat 

 remote from the end; apical setae unusually strong, almost spiniform, the inner 

 medial one nearly attaining half the length of the body and, like the outer one, 

 quite smooth in its proximal half, the remaining part being clothed with shoi 

 coarse hairs; seta of inner corner only slightly longer than that of the outer. 

 Anterior antennae scarcely as long as the cephalic segment, and composed of the 

 normal number of joints (17). Posterior antennae with the terminal joint m 

 longer than the penultimate one. Natatory legs comparatively strongly built 

 terminal joint of outer ramus in all of them armed outside with 3 coarse spin< 

 and having the normal number of setae inside; seta attached outside the termim 

 joint of the inner ramus in 1st pair of normal appearance, in the other pairs, 

 however, transformed into a strong denticulated spine ; apical spines of same ramus 

 in 4th pair subequal in size. Last pair of legs somewhat resembling those in 

 C. vulgaris, the proximal joint being considerably expanded, and the distal joint 

 of inconsiderable size, with the lateral spine very minute. Ovisacs of moderate 

 size and oval in form, being only slightly divergent. Seminal receptacle trans- 

 versely elliptical in form, and only very slightly produced behind. 



Colour light yellowish brown. 



Length of adult female 1.20 mm. 



Remarks. Dr. Schmeil does not admit the specific validity of this form, 

 which he only regards as a variety of the preceding species. I think, however, 

 that it ought to be kept apart, and Lilljeborg has also, in his account of the 

 Swedish Cyclopses, described it as a well-defined species. It may indeed readily 

 be distinguished from C. lucidulus by its much more robust body, for which 

 reason also the specific name robustus was proposed by the present author. In 

 the structural details also several well-marked differences are found to exist, as 

 shown in the above-given diagnosis. According to Lilljeborg, the North American 

 form C. brevispinosus Herrick is identical with the present species. 



Occurrence. This form seems in our country to be of rather rare occur- 

 rence. I have only met with it quite occasionally at the border of 3 of our 

 larger lakes, viz., the Nordsj0 Lake, Maridal Lake and Mj0sen. In habits it is 

 a true bottom-form, keeping constantly close to the ground. 



Distribution. Sweden (Lilljeborg), North America (Herrick). 



