35 



Occurrence. I first found this species in the Mariclal Lake near Christiania, 

 where it occurred only in the deepest part of the lake, at the considerable depth 

 of 40 50 fathoms; hence the specific name proposed. Prof. Brady has taken it 

 under quite similar circumstances in some 'of the British lakes. Besides in the 

 Maridal Lake, I have observed this form in the Vansj0, near Moss, and in the 

 Stensfjord, a branch of the great lake, Tyrifjord. In the last-named locality it 

 occurred rather frequently at depths varying from 6 to 12 fathoms, muddy bottom. 

 The specimens from all 3 localities agree perfectly with each other, and the 

 figures given by Prof. Brady show the British form also to be in full accordance 

 with the Norwegian one. 



Distribution. Sweden (Lilljeborg), British Isles (Brady), Central Asia 

 (the present author). 



16. Cyclops lacustris, G. 0. Sars. 



(PI. XVIII). 

 Cyclops lacustris, G. 0. Sars, 1. c., p. 30. 



Specific Characters. Female. Body moderately slender, with the anterior 

 division oblong oval in form, greatest width about half the length and occurring 

 somewhat in front of the middle. Cephalic segment comparatively large, with the 

 frontal part almost transversely truncated. Lateral parts of penultimate trunk- 

 segment not at all produced, being of the very same appearance as in the 2 

 preceding segments. Last trunk-segment likewise only very slightly prominent 

 laterally. Uenital segment of a rather characteristic form, being considerably 

 longer than it is broad and abruptly narrowed in the middle, with the anterior 

 part moderately dilated, the posterior part cylindric in shape. Caudal rami not 

 attaining the length of the 3 preceding segments combined, and slightly divergent, 

 dorsal keel obsolete, inner edge very finely ciliated, seta of outer edge small and 

 not very far from the end, apical setse rather slender, the inner medial one 

 attaining fully the length of the tail, seta of inner corner more than twice as 

 long as that of the outer. Anterior antennae rather slender, reaching, when 

 reflexed, beyond the 2nd segment of the body. Anterior maxillipeds with the 

 claw of the 2nd basal joint unusually slender. Natatory legs exhibiting an arma- 

 ture similar to that in the 2 preceding species, rami comparatively slender, with 

 very long setae; outer apical spine of inner ramus in 4th pair rather small, 

 scarcely exceeding 1 / 3 of the length of the inner. Last pair of legs with the 

 distal joint rather narrow, sublinear in form, lateral spine extremely minute and 

 attached at about the middle of the inner edge, apical seta, on the other hand, 



