155 



Colour not yet ascertained. 



Length of adult female 1.65 mm., of male 1.15 in in. 



IteiiHtrk*. This form, though nearly allied to the typical species, is un- 

 questionably distinct, differing, as it does, not only in the more slender form of 

 the body and the gibbously produced frontal part, but also in the greater length 

 of tlu> anterior antennae, and the more slender form of the natatory legs. 



Occurrence. -This form occurred not unfrequently in some of the plankton- 

 samples taken during the cruise of the "Michael Sars", 1900, in the open sea 

 between Finmark and Bear Island; but as the specimens were more or less 

 damaged, and moreover, as shown by the structure of the urosome, hnd not 

 arrived at sexual maturity, their specific difference from P. rlongatus was less 

 apparent, for which reason I at first only regarded this form as a variety of the 

 typical species. It was only by the examination of another sample taken by 

 Mr. Amundsen early in the spring of the following year from about the same tract, 

 that I could convince myself of the distinctness of the present form. This sample 

 contained several fully adult and admirably preserved female specimens with 

 the rather large ovisac still attached to the genital segment, and also some few 

 adult male specimens. In the same sample a number of comparatively large, 

 and likewise ovigerous, specimens of P. elongates also occurred, and it was very 

 easy to distinguish between these 2 species, on account of the rather different 

 shape of the frontal part, and the difference in the length of the anterior antennae. 

 That this undoubtedly true arctic form also occasionally occurs in the immediate 

 neighbourhood of the Norwegian coast, was proved by the examination of one 

 of the plankton-samples taken during the cruise of the ,,Michael Sars" in the 

 Lyngenfjord, Finmaik. This sample contained some young specimens of a 



x evidently belonging to the present species. 



The following genus is also to be added: 



Microcalanus, a. o. Sars 1901. 



Syn: Pseudocalanus, G. 0. Sars (part). 



Generic Characters Body of comparatively small size, and rather short 

 and compact form, recalling that of Paracalanm. Cephalosome completely coa- 

 lesced with the 1st pedigerous segment; front carrying 2 extremely small tenta- 

 cular appendages below. Urosome in female comparatively short, with the genital 

 segment more or less dilated, in male considerably more slender. Caudal rami 



