141 



oblong oval in form, and, in addition to the apical bristles, provided with '2 

 finely ciliated seta? on the inner edge. 



Body in female of a clear yellowish grey colour, with translucent olive- 

 green ovarial cells and likewise greenish ovisacs; that of male highly pellucid, 

 exhibiting within the anterior part scattered reddish-orange oil-bubbles; eye 

 much larger than in female, and bright red. 



Length of adult female amounting to 1.10 mm., of male to 0.00 mm. 



Remarks. The female sex of this peculiar Copepod has long been known; 

 but it is only in recent times that the existence of the male sex has been satis- 

 factorily ascertained. True, a male specimen w r as observed by Clans as early 

 as the year 1880; but its relation to Cancerilla tiibnlata of Dalyell was not 

 recognised by that author, who did not hesitate to establish for it, not only a 

 new species, but even a new genus. There cannot in my opinion be any doubt, 

 that Giesbrecht was quite right in considering Caligidium vagabnndiim of Clans 

 to be the adult male of Cancerilla tnbulata, and that the description and figure 

 given by Canu of the supposed male Cancerilla only refer to a quite immature 

 specimen. The remarkable sexual dimorphism occurring in the present form 

 may be easily explained from the sedentary habits of the female, causing in the 

 latter a considerable reduction of the sensory and locomotory apparatus, and at 

 the same time affecting the general form of the body. 



Occurrence. I have met with the female of this curious form occasio- 

 nally, off both the south and west coasts of Norway, and always attached in the 

 very same manner ventrally to the base of one of the arms of the common 

 brittle-star, Amphiiira sqiiamata. Its attachment is effected by the strongly hooked 

 posterior antennae, and is so firm that it is very difficult to detach it without 

 breaking off those appendages. It is indeed very probable that the animal 

 remains attached in the place it has chosen for the rest of its life, being quite 

 unable to move about in the water. The adult male I have taken free in the 

 sea in 3 different localities of the Norwegian coast, viz., at Risor and Korshavn, 

 on the south coast, and at Magero, outside the Trondhjem Fjord, only a single 

 specimen being found in each locality. 



Distribution. British Isles (Dalyell), coast of France (Canu), Mediter- 

 ranean, at Trieste (Glaus) and Naples (Giesbrecht). 



19. Crustacea. 



