present on the terminal joint in the 2nd and 3rd pairs. Setae of last pair of 

 legs much shorter than in female. 



Body in both sexes highly pellucid and nearly colourless, though in adult 

 females generally a light orange pigment is seen clothing the oral area and partly 

 also the sides of the head. A large oil-bubble is often found within the posterior 

 part of the trunk, and 2 smaller ones at the limit between the head and the 

 1st pedigerous segment. 



Length of adult female 1.35 mm., of male 0.82 mm. 



Remarks. I regard it as beyond all doubt that the above-described form 

 is that originally recorded by Glaus under the name Oithona spinirostris. It has 

 generally been confounded with the very nearly allied species described by Baird 

 as 0. plumifera, from which, however, it is at once distinguished by the absence 

 of the very conspicuous brightly-coloured plumes projecting in the latter at each 

 side of the trunk, and from which indeed the specific name plumifera has been 

 derived. These plumes in reality belong to the natatory legs, and are formed 

 by the setae attached outside the 2nd basal joint of the legs, which in the said 

 species are richly plumose, whereas in the form here under consideration they 

 ars simple and do not even project laterally. In addition to this distinguishing 

 character, Mr. Farran has recently pointed out some minute differences in the 

 structure of the oral parts between these two forms, which accordingly must be 

 regarded as distinct, though closely- allied species. Mr. Farran has proposed a 

 new specific name for the present species, viz., atlantica, but I think that his 

 doubt about the identity of Glaus' species with the one here under question cannot 

 properly be approved. 



Occurrence. I have observed this form in many different places on the 

 Norwegian coast, at least up to the Trondhjem Fjord. It is, however, not nearly 

 so common as the next species, and seems more properly to be an inhabitant of 

 the open sea, from which it is only occasionally brought in by the currents to 

 the shores and fjords. 



When kept living in a vessel with fresh sea-water, the specimens are 

 always found freely suspended in the water, more generally in an erect attitude, 

 with the anterior antennae and the caudal setae spread to each side, these parts 

 apparently serving as a very effective balancing apparatus. In this attitude the 

 animal often rests for long time nearly immobile, only now and then, by 

 the action of the natatory legs, making a short bound to change its place. To 

 judge from the structure of the oral parts, the animal must be of a, very rapacious 

 nature, probably feeding upon other small pelagic animals. These may at 

 first be seized by the slender maxillipeds and by them thrown in against the 



