42 



appearance. Caudal rami, however, conspicuously more produced, even exceeding 

 in length the last 3 segments combined, and only very slightly divergent; iniddh 

 apical setse rather slender, the inner one being considerably longer than the tail, 

 seta of inner corner comparatively shorter than in C. vulgaris, not attaining twice 

 the length of the outermost one Both pairs of antennae of a very similar structure 

 to that in the said species. Natatory legs likewise rather similar; apical spines 

 of inner ramus in 4th pair, however, conspicuously more slender. Last pair of 

 legs, as in C. vulgaris, with the proximal joint rather expanded and conically 

 produced outside, distal joint, however, comparatively narrower, with the lateral 

 spine almost obsolete. Ovisacs very large and of a somewhat irregular form, 

 projecting far beyond the caudal rami, and less divergent than in C. vulgaris. 

 Seminal receptacle with the anterior part comparatively larger than in that species, 

 occupying almost the whole width of the genital segment. 



Colour light yellowish brown, with a more or less distinct olivaceous or 

 greenish tinge. 



Length of adult female amounting to 2.50 mm. 



Remarks. This form has been considered by Dr. Schmeil and several 

 other authors to be only a large variety of the preceding species. Lilljeborg has, 

 however, vindicated its specific distinctness, and I have myself, by a careful com- 

 parison, come to the same result. It may be at once distinguished from C. vul- 

 garis, not only by its unusually large size, but also by the much more produced caudal 

 rami, and by the somewhat different mutual relation in the length of the apical setse. 

 The last pair of legs also, though somewhat resembling those in the said species, 

 differ slightly in the shape of the distal joint. Finally, the seminal receptacle 

 is of a somewhat different shape, as shown by the figure here given. The North 

 American form C. ingens of Herrick seems to be referable to the present species. 



Occurrence.! have taken this form in great abundance from some small 

 ponds near Christiania. The specimens were observed early in the spring, even 

 before the ice was wholly melted, and as all of them at that time were fully 

 grown and to some extent thickly covered with Epizoa, they must have developed 

 at a much earlier period, during the winter. Later in the spring their number 

 decreased gradually, and at the approach of the summer they seemed wholly to 

 have disappeared. The species also occurs in some of our larger lakes and more 

 generally in very considerable depths. In Lake Mj0sen I have even taken it 

 at the great depth of 100 fathoms ; and though most of the specimens there 

 obtained were immature, they could with full certainty be adduced to the present 

 species, on account of the considerably produced caudal rami. Lilljeborg has 

 found the species under quite similar circumstances in some of the Swedish lakes. 



