47 



more irregularly arranged, and wanting on the last joint. 5th pair of legs some- 

 what curved, with the inner edge of the basal joint densely spinulose, 2nd joint 

 conspicuously dilated in the middle, almost globose, and slightly spinulose inside, 

 terminal joint about the same length but much narrower, and armed in mature speci- 

 mens with 4 short ciliated spines, 2 apical and 2 lateral. These legs in younger 

 specimens of rather different appearance, the 2 outer joints being confluent to 

 an angularly curved piece carrying only 3 spines on the tip. 



Male considerably smaller than female and of more slender form, with 

 the lateral lobes of last segment of metasome less prominent. Urosome very 

 narrow, and comparatively longer than in female, caudal rarni mobile. Anterior 

 antennse modified in the usual manner. Oral parts less rudimentary than in most 

 other Amphascandria. Left leg of last pair exceedingly slender, with the 4th 

 joint very narrow, linear, and longer than the last 2 joints combined; right leg 

 distinctly developed, though very small, reaching about to the end of the 2nd 

 joint of the left. 



Colour. Body in both sexes whitish, pellucid, tinged in some places with 

 a slight reddish pigment. 



Length of adult female 3.50 mm., of male 2.50 mm. 



Remarks. This form was first described by the present author from a 

 somewhat defective female specimen procured during Nansen's Polar Expedition. 

 The apparent differences in the general form of the body, and especially in the 

 structure of the last pair of legs, between the polar specimen and the Norwegian 

 form here described, may be accounted for by the circumstance that that specimen 

 was not fully mature, though of rather large size. I have found similar differences 

 in young specimens of the Norwegian form. The present species is easily dist- 

 inguished from the type species, X. agilis, Giesbrecht, both by its much larger 

 size and by several other characters, for instance, the presence in the male of a 

 right leg in the last pair. 



Occurrence. I have found this form not infrequently in the Stavanger 

 Fjord, at Jelso and Sunde, as also in a few other places off the west coast of 

 Norway. The specimens were only procured by the aid of the dredge from very 

 considerable depths, down to 400 fathoms, where it occurred together with Chiri- 

 dius armatus, Boeck. The character of this Calanoid as a relict arctic form has 

 been proved by the occurrence of a specimen of apparently the same species in 

 the Polar Sea, at a far less depth. 



Distribution. Polar basin, north of the New Siberian Isles (a solitary 

 young female specimen). 



