26 AXEL OHLIN, AKCTIC CRUSTACEA. 



free segments of tlie pleon except tlie terminal one, but only 

 three in Ch. wcf/alnrti. 



In tbis form there is, on the ventral side of tlie seventh 

 segment of the pereion, in the middle line a sharp point. It 

 is triangulär on the anterior and lateral sides, and with a 

 rather deep groove on the anterior side, as indicating its 

 formation by the eoalescence of the two crisfce stcrnales which 

 run along the midst of the ventral surface of the other seg- 

 ments of the pereion in this and other species of the genus, 

 thus forniing a slight median groove. Even in small speci- 

 mens this process is clearly to be distinguished. In Ch. So- 

 hini there is instead of that point a deep excavation as in 

 the preeeding segments. 



In regard to the size and colour, I cannot agree with 

 Särs in regarding them as characteristics of specific value. 

 As to the size, which Särs says is less in Ch. Sohini than 

 in Ch. nicgahira. 1 have myself in the year 1894 trawled 

 specimens of Ch. Sahini which are far larger than the largest 

 of Ch. megalura, and I have measured a specimen of the same 

 species from Baffin Land of SO mm. length, thus far exceed- 

 ing those of Ch. megalura from the Norwegian Xorth At- 

 lantic expedition (50 mm.). 



The colour of this form seems to be subjected to no less 

 variations than other Idotheids. In the same haul from Bi- 

 loculina bottom I found not only specimens of an uniform 

 grayish colour. like those described by Särs, 'but also a good 

 deal of brown-yellowish individuals. 



Nevertheless I would perhaps regard this form as a mere 

 variety of Ivröyer's type species, if there was not a striking 

 difFerence in regard to its horizontal and bathymetrical dis- 

 tribution. In his -Evertebratfaunan i Sibiriens Ishaf» Stux- 

 berg has given in detail an intere.sting study of the geo- 

 graphical range of Ch. Sahini and Ch. enfovion which seems 

 still to be exa et. It is stated by that exposition that the 

 former species is nearh' circumpolar. The onty parts of the 

 Arctic Ocean where it has not yet been recorded are the 

 Behrings Sea, the adjacent parts as far as long. 170° E., and 

 the sea between Spitzbergen and Greenland. As to the Beh- 

 rings Sea, it seems very likely that its non-oecurrence there 

 depends only on the relatively scarce researches, the natural 

 conditions being, at least near to the coast, more or less the 



