200 



Adult male more slender in form than female, with the cephalon less 

 broad in front. Genital segment widening distally, and generally containing 2 

 well-marked spermatophores. Anterior antennae of exactly same structure as 

 in female. Posterior antennae however much smaller than in female, though 

 built in a similar manner. Posterior maxillipeds rather slender, with the 

 dactylus very long and nearly straight, terminating in an obtuse point. 



Body in both sexes rather pellucid, with very dark translucent intestine, 

 and moreover exhibiting a bright blue pigment chiefly accumulated in the 

 anterior part. 



Length of young female, immediately before affixion, 1.30 mm.; that 

 of adult male 1.10 mm. 



Remarks. The adult ovigerous female of this form was first described 

 by Nordman in the above-quoted treatise, and has subsequently been more 

 closely examined by several other authors. The male and the still free-living 

 female are far less fully known, and I hope therefore that the description and 

 figures here given will be of some interest. 



Occurrence. In the adult state, as above mentioned, the female of 

 this form is found firmly attached by the strongly clawed posterior antennas 

 to the gills of various fresh-water fishes, and when once attached in this 

 manner, it scarcely at all leaves its hold. In the juvenile state, however, it 

 is a vagabond animal, swimming about, like the always free-living male, near 

 the surface of the water in company with other free-living Copepods, from 

 which it may at once be recognized by the bright blue pigment accumulated 

 within the anterior part of the body. In this free-living state I have taken the 

 present Copepod occasionally among plankton collected from some of our 

 larger lakes. It is very likely to believe, that the female is fecundated by the 

 male before its affixion. 



Distribution. Lakes of Sweden, Russia and central Europa. 



Fam. 15. Clausiidae. 



General Characters. Body more or less elongated and narrow, with 

 no sharp demarkation between the anterior and posterior divisions; the latter 

 composed (in female) of the normal number of segments. Anterior antennae 

 small, attenuated. Posterior antennae comparatively short, but distinctly pre- 



