114 



Last pair of legs of a structure similar to that in M. longa, but with the 

 terminal joint on both leg's less attenuated distally. 



Colour. Body in both sexes highly pellucid, and almost colourless. 



Length of adult female 2.50 mm., of male 2.30 mm. 



Remarks. This form is closely allied to M. longa, but is of much inferior 

 size, and moreover easily distinguished by its somewhat less slender form, the 

 shorter caudal rami, and the much more strongly vaulted cephalosome. Finally, 

 the last pair of legs in the female are only 3-articulate, the outer 2 joints being 

 confluent. The form described by Brady in his work on the British Copepoda 

 as M. armata is unquestionably the present species. It was subsequently recorded 

 by the same author under another name, viz., Paracalanus hibernicus, and Dr. 

 Giesbrecht in his great work records it as Mctr'nlla hibernica, not being at that 

 time aware of its identity with Boeck's species. 



Occurrence. Whereas M. longa must be regarded as a true Arctic form, 

 the present species is evidently of a more southern range. I have found it rather 

 commonly along the south and west coasts of Norway and, unlike what is the 

 case with M. longa, it is often met with near the surface of the sea. It extends 

 northwards at least to the Lofoten Islands, and it was also found in some of the 

 plankton-samples taken in the open sea during the cruise of the "Michael Sars". 

 On the other hand, I have never found it in any samples from the Arctic Ocean. 

 The luminous property of this form is mentioned by Boeck, who for this reason 

 proposed for it the specific name lucens. 



Distribution. British Isles (Brady), Iceland, Faroe Channel (Norman), 

 Atlantic Ocean between lat. 50 and 62 N. (Cleve). 



Gen. 19. PleurOITiamma, Giesbrecht, 1898. 



Syn: Pleuromma, Glaus (not Doneschall). 



Generic Characters. Form of body generally less slender than in Metrulia. 

 in some cases rather different in the two sexes. Cephalosome with a very conspi- 

 cuous dark-coloured mammilliform knob (luminous organ) on right side, at the base 

 of the posterior maxillipeds, rostral prominence generally with 1 or 2 dentiform 

 ledges in front, tentacular appendages shorter than in Metridia. Lateral parts 

 of last segment of metasome rounded off. Urosome less slender than in Metridia, 

 with the genital segment in female considerably protuberant below; anal segment 



