10 



with the dorsal one, a perfectly even curve. Lateral corners of last pedigerous 

 segment slightly produced, but rounded at the tip. Urosome about half the length 

 of the metasome; caudal rami somewhat longer than the anal segment. Anterior 

 antennae, when reflexed, extending beyond the caudal rami by about the last 3 

 articulations. 



Male. Cephalosome more sharply defined behind than in female, forming 

 at the end dorsally a small gibbous projection, and distinctly carinated above, 

 frontal part somewhat more prominent; lateral corners of last pedigerous segment 

 less produced. Urosome rather slender, with the 2nd segment much the largest. 

 Subapical plumose setse of anterior antennae less developed than in female, and 

 somewhat uneqal in length. Last pair of legs with the outer rami not very 

 different in appearance, the left one, however, somewhat longer than the right, 

 with the terminal joint obpyriform in shape and nearly as long as the proceeding 

 joint, corresponding inner ramus reaching beyond the middle of the 2nd joint of 

 the outer one. 



Colour. Body pellucid, more or less tinged with light red, anterior 

 antennae often bright red. 



Size. Usual length of adult female about 4 mm., of male 3.60 mm. 

 Maximum length of arctic specimens 5 mrn. 



Remarks. This is apparently the form at first recorded by Gunnertis as 

 Monoculus finmarchicus. It has, however, been confounded by most authors with 

 the succeeding nearly-allied species, from which, on a closer examination, it may 

 be easily distinguished in both sexes, chiefly by the more evenly rounded frontal 

 part, the longer caudal rami, and the less elongated outer ramus of the left last 

 leg in the male. It 'also attains a considerably larger size than does the above- 

 mentioned species. The 2 supposed species described by Kroyer as Calanus 

 spitsberyensis and C. qrinqueannulatus are unquestionably both referable to the 

 present species, the former being the female and the latter the male. 



Occurrence. Of all the marine Calanoids of Norwa}^ this form is by far 

 the most common, occurring often in enormous shoals, and thus sometimes giving 

 the sea a conspicuously reddish hue. It is found everywhere in the open sea, 

 more frequently at the very surface, though at times it may also descend to 

 greater depths, or be carried by the waves and currents towards the shores or 

 into the bays and fjords. Off the Norwegian coast, I have met with it from 

 Vads0 to Jsederen (Tananger) ; but farther east it seems to be superseded by 

 the succeeding species. It moves rather rapidly, with abrupt bounds caused by 

 energetic strokes of the natatory legs. At times, however, it is seen quietly 

 suspended in the water, with the anterior antennae spread out to each side at right 



