11 



angles to the body, or proceeding slowly by rapid vibrations of the posterior 

 antennae and the mandibular palps. The male is still more agile than the female, 

 and the motion effected by the posterior antennae and mandibular palps is more 

 energetic, in accordance with the somewhat stronger development of these appen- 

 dages and the pertaining muscles, being changed to a somewhat jerky leap 

 through the water. At some seasons male specimens are by no means rare, 

 though the female sex always preponderates considerably in number. This Calanoid 

 is eagerly devoured by some of our common food-fishes, for instance the herring 

 and the mackerel, and in some cases, as stated by Prof. Eob. Collett, forms almost 

 the exclusive nourishment of one of our great whales, Balcenoptera borealis. 



Distribution. The present species seems to be especially characteristic 

 of the arctic zone, occurring abundantly in almost all samples of plankton taken 

 in that part of the Ocean, from Greenland in the west to the Behring Islands in 

 the east. In the icy Polar basin crossed by Nansen, it occurred everywhere, and 

 often in great abundance, up to and beyond 85 of latitude. The former statements 

 about the extraordinarily wide distribution of the present species southwards, 

 cannot be regarded as reliable, owing to its having been confounded with the 

 succeeding species. 



2. Calanus helgolandicus, (Glaus). 



(PI. IV.) 



Cetochilus helgolandicus, Claus, Die frei lebenden Copepoden, p. 171, PI. XXVI, figs. 29. 

 Syn: Calanus finmarchicus, Brady, Giesbrecht etc. (not Gunnerus). 



Specific Characters. Female. Anterior division of body, seen dorsally, 

 narrow oblong in form, greatest width not attaining 1 / 3 of the length, frontal part 

 angularly produced between the insertions of the anterior antennas ; seen laterally, 

 scarcely dilated at all anteriorly, frontal margin abruptly and narrowly curved. 

 Lateral corners of last pedigerous segment but very slightly produced and obtusely 

 rounded. Urosome exceeding half the length of the metasome, caudal rami rather 

 short, scarcely longer than the anal segment. Anterior antennae, when reflexed, 

 reaching beyond the caudal rami by about the last 2 articulations. Male resembling 

 that of the preceding species, but having the frontal part considerably more pro- 

 duced. Last pair of legs more asymmetrical, the outer ramus of left leg being 

 considerably elongated, with the terminal joint scarcely exceeding half the length 

 of the penultimate one, inner ramus extending but little beyond the 1st joint of 

 the outer ramus. Body in both sexes very pellucid, with a slight reddish pigment 



