30 



The male, too, differs conspicuously not only in its small size, but also in the 

 much more feeble and simple structure of the last pair of legs. 



Occurrence. Specimens of this arctic species were found in some of the 

 plankton-proofs taken last year during the cruise of the " Michael Sars". It occurred 

 at 2 different Stations (Nos. 8 & 9), located in the open sea, about midway 

 between Iceland and Norway, the depth being recorded to be from 200 to 800 

 metres. Considering these finding-places, I feel justified in refering the present 

 species to the fauna of Norway, though it has not as yet been found in the 

 immediate vicinity of the coast. 



Distribution. The Polar basin crossed by Nansen, in many places rather 

 abundantly, from the surface down to a depth of 300 metres. 



11. Chiridius tenuispinus, G. 0. Sars. 



(PI. XVIII.) 

 Chiridius tenuispinus, G. 0. Sars, The Norw. North Polar Expedition. Crustacea, p. 67, PI. XVIII. 



Specific Characters. Female. Body comparatively less slender than in 

 the 2 preceding species, with the urosome much shorter, scarcely exceeding in 

 length */4 of the anterior division. Front projecting below in a sharply-pointed, 

 but short rostrum. Last segment of metasome produced on each side to a very 

 slender spiniform process pointing straight behind. Caudal rami comparatively 

 short, only slightly longer than they are broad, and rounded at the tip. Anterior 

 antennae, when reflexed, reaching about to the end of the 2nd caudal segment. 

 Posterior antennae with the inner ramus rather produced and very narrow, though 

 shorter than the outer. Posterior maxillipeds still more slender than in the 2 

 preceding species. First pair of legs having the 1st joint of the outer ramus con- 

 fluent with the 2nd, and without any spine outside. Inner ramus of 2nd pair 

 distinctly biarticulate, that of the 2 succeeding pairs 3-articulate, with all the 

 joints well defined. Male unknown. Length of adult female 3.80 mm. 



Remarks. This species, first described by the present author from Nansen's 

 Polar Expedition, is closely allied to a form recorded by Dr. Giesbrecht from the 

 Pacific under the name of Oa'idius pungens, and both these forms are unquestionably 

 congeneric. The northern form differs, however, in the more slender form of the 

 spiniform projections issuing from the last segment of the metasome, and more 

 especially in the fact, that the inner ramus of the 2nd pair of legs is distinctly 

 biarticulate, whereas in the Pacific species it is uniarticulate. In my opinion the 

 ganus Oa'idius can scarcely be supported, as the characters upon which it is 

 founded, have proved to vary in different species of the present genus. I have 



