75 



appearance; seta of inner corner scarcely more than half as long as the corre- 

 sponding ramus, though longer than the spine of the outer corner; the latter 

 comparatively short and thick. Anterior antennae less elongated than in the 

 preceding species, scarcely reaching, when reflexed, beyond the middle of the 

 2nd segment, lateral rib of the outer joints very finely denticulated in the proximal 

 part of last joint, otherwise quite smooth. Posterior antennae and oral parts 

 scarcely different in structure from these parts in the preceding species. Nata- 

 tory legs rather strongly built, but likewise of the usual structure. Last pair of 

 legs with the spine of the inner edge comparatively shorter than in L. Lilljeborgi, 

 but much thicker and coarsely denticulated. Ovisacs rather large and somewhat 

 divergent. Seminal receptacle with the anterior part less broad than in the last 

 described species. 



Colour light yellowish grey. 



Length of adult female amounting to 1.30 mm. 



RemarTcs, This species is nearly allied to L. Lilljeborgi^ but may be 

 easily distinguished by the very narrow and prolonged caudal rami and by the 

 somewhat shorter anterior antennae. It also grows to a considerably larger size 

 than that species. The North American form, Cyclops elegans Herrich, of which 

 I have had specimens for examination, is not, as opined by Lilljeborg, identical 

 with the present species, as it has the anterior antennae much more elongated 

 and also exhibits some differences in the structure of the caudal rami and of 

 the last pair of legs. 



Occurrence. I have only met with this species in large lakes, for instance, 

 in the Maridal Lake near Christiania, and in the great lakes Mj0sen and Tyri fjord. 

 It is generally found at a depth of a few fathoms, near the margin, but in some 

 cases it descends to much greater depths. In Lake Mj0sen I have for instance 

 taken it occasionally down to 50 fathoms. 



Distribution. Sweden (Lilljeborg), peninsula of Kola and northern part 

 of Siberia (same author). 



45. Leptocyclops macrurus, G. 0. Sars. 



(PI. XLVII). 



Cyclops macrurus, G. 0. Sars, 1. c. p. 45. 

 Syu: Cyclops maarensis, Vessel er. 



Specific Characters. Female. Body rather slender, with the tail much 

 produced and only slightly shorter than the anterior division. Caudal rami ex- 

 ceedingly long and narrow, almost attaining the length of the whole remaining 



