107 



Occurrence. I have met with this beautiful Calanoid in many places in 

 Norway, in the lowland, and especially in the mountain lakes. According to the 

 recent investigations of Mr. Huitfeldt-Kaas, it is generally distributed in almost 

 all the lakes of the western part of Norway, and it has been found occasionally 

 by Mr. Rabot in the great lake Rosvand in Nordland. The most northerly place 

 where I have met with it, is at Bodo, located somewhat north of the Arctic 

 Circle. As a rule, it is found as a true limnetic form in larger lakes, where it 

 constitutes an essential food of the trout; but occasionally it also occurs in 

 comparatively small tarns and ditches. It moves in a peculiar jerky manner, 

 chiefly by rhythmical strokes of the posterior antennae, only now and then making 

 a quick bound by employing its natatory legs and urosome. The specific name 

 proposed by Prof. Lilljeborg refers to this peculiar motion. 



Distribution. Lakes of Sweden (Lilljeborg), Russia (Poggenpol), central 

 Germany (Gruber, etc.), Bohemia (Fric), North Italy (Pavesi), Switzerland (Imliof). 



46. Heteroeope borealis (Fischer). 



(PI. LXXIII). 



Cyclops'ma borealis, Fischer, in ..Middendorf's Sibirische Reise". Zoul. p. 158. 



PL VIII, figs. 4046. 



Syn : Heteroeope robusta, Gruber (not G. 0. Sars). 

 saliens, Noi-dqvist (not Lilljeborg). 



Weismanni, Imhof. 



Specific Characters. Female. Body considerably more robust than in the 

 preceding species, with the anterior division, seen dorsally, oval in form, greatest 

 width nearly attaining half the length, and occurring about in the middle. Uro- 

 some about the length of the metasome, genital segment fully as long as the 

 other 2 combined, hind part of genital area with a slight incurved dentiform 

 projection on each side, anal segment shorter than the middle one. Caudal rami 

 short and broad, widening distal ly, and slightly divergent, apical setae conspi- 

 cuously dilated at the base, the middle one somewhat longer than the other 2, 

 bristle outside them comparatively larger than in H. saliens, attaining the length 

 of the caudal rami. Anterior antennae, when reflexed, reaching but little beyond 

 the genital segment. Last pair of legs with the terminal joint comparatively 

 narrower than in H. saliens, and having the denticles of the inner edge less 

 distinctly bidentate, apical spine very slender 



Male resembling that of H. saliens, but more robust of form, with the 

 middle section of right anterior antenna more tumefied. Outer ramus of 2nd to 



