117 



Occurrence. I have met with this beautiful form in several places both 

 on the south and west coasts of Norway, as also in the Trondhjem Fjord, but 

 nowhere in any considerable number. It is generally found in depths ranging 

 from 6 to 20 fathoms among Laminarise and other algse. The movements of the 

 animal are particularly rapid and graceful. 



Distribution. British Isles (Brady), Mediterranean (Glaus), Gulf of Suez 

 (A. Scott), Ceylon (same author). 



Gen. 30. Hall thai 6StriS, G. 0. Sars, n. 



Generic Characters. -Body elongated, subcylindrical in form, with no sharp 

 demarcation between the 2 chief divisions. Cephalic segment comparatively small 

 and somewhat depressed, rostrum short, but uell defined at the base. Epimeral 

 plates poorly developed. Urosome very large and massive, with the caudal rami 

 unusually prolonged and divergent. Eye normal. Anterior antennre of usual 

 structure, 9-articulate. Posterior antennae with the outer ramus rather narrow, 

 biarticulate. Oral parts on the whole normal; posterior maxillipeds, however, 

 unusually compact. 1st pair of legs resembling in structure those in Thalestris. 

 Natatory legs likewise of a very similar structure. Last pair of legs of moderate 

 size, with the distal joint the more prominent. 



Remarks. This new genus is founded upon the peculiar form first recorded 

 by Kroyer as Harpacticus Groni, and subsequently described by Brady under the 

 name of Thalestris serrulata. According to the structure of the 1st pair of legs, 

 this form is indeed more nearly related to Thalestris than to Harpacticus, and 

 unquestionably belongs to the family Thalestridcc. It cannot however properly be 

 referred to the genus Thalestris in the restriction here adopted, and it also dif- 

 fers very markedly from the other Thalestridse, both in its whole external ap- 

 pearance and more particularly in its habits, it being one of the few Harpac- 

 ticoida, which leads a true pelagic life. The generic name here proposed refers 

 to this latter peculiarity. 



16 Crustacea. 



