36 



unusually long and slender. Ovisacs small, rounded, and each containing a very 

 limited number of ova. Seminal receptacle comparatively larger than in C. abys- 

 sorum, anterior part evenly rounded, posterior part rather produced. Spermatophores 

 attached to the genital opening of about the same appearance as in C. strenuus. 



Body highly pellucid, with a very faint bluish or greenish tinge. 



Length of adult female 1.50 mm., of male 1.30 mm. 



Remarks. In the case also of the present form the specific validity has 

 not been admitted by recent authors, though in my opinion it is a very well-defined 

 species. Lilljehorg was inclined to regard it as a variety of C. strenuus, which 

 has adapted itself to a limnetic life. On a closer examination, however, the 

 well-marked differences which this form exhibits cannot by any means be explained 

 in this way, nor be regarded as simply accidental or varietal. 



Occurrence. I have only met with this form in our 2 largest lakes, 

 Mj0seri and Tyrifjord. It lives there as a true limnetic form together with Limno- 

 calanus macrurus and other midwater forms, being generally found swimming 

 about close to the surface of the water. 



Distribution. Sweden (Lilljeborg). 



17. Cyclops scutifer, G. 0. Sars. 



(PI. XIX). 

 Cyclops scutifer, G. 0. Sars, J. c., p. 28. 



Specific Characters. Female. Body comparatively slender, with the 

 anterior division narrow oblong in outline, greatest width scarcely attaining half 

 the length, and occurring somewhat in front of the middle. Lateral parts of the 

 last 2 trunk-segments greatly produced, being expanded to triangular exstant 

 lamellae, which are more or less contiguous, so as to present, together with the 

 corresponding segments, the appearance of a quadrangular shield obtecting the 

 posterior part of the trunk. Genital segment comparatively large and very much 

 dilated in front, with a small knob-like prominence on each side, posterior part 

 gradually narrowed. Caudal rami scarcely longer than the last 2 segments combined 

 and only very slightly divergent, dorsal keel only faintly indicated, inner edge 

 finely ciliated ; seta of outer edge rather remote from the end, apical setae very 

 unequal in length, the inner medial one much the longest, seta of inner corner 

 more than twice as long as that of the outer. Anterior antennae rather slender, 

 reaching, when reflexed, considerably beyond the 2nd segment of the body, and 

 clothed with comparatively long setae. Posterior antennae with the terminal joint 

 scarcely longer than the penultimate one. Anterior maxillipeds resembling in 



