Body in both sexes extremely pellucid, without any obvious pigment. 



Length of adult female 0.700.90 mm.; of male 0.500.60 mm. 



Remarks. There cannot in my opinion be any doubt, that the form at 

 first recorded by Glaus as 0. helgolandica is the present species. It has subse- 

 quently been redescribed by the same author from Mediterranean specimens, but 

 under another specific name, viz., similis, and this name has been applied to the 

 present species by most authors. According to the rules of priority, however, 

 the first name under which a species has been recorded should in every case be 

 retained. The 2 forms named by Boeck 0. spinifrons and 0. pyymcea are un- 

 doubtedly both referable to the present species, and this is also the case with 

 the form described by Dr. Giesbrecht from the bay of Kiel as 0. spinirostris. 

 The present species is easily distinguishable from the preceding one by the rather 

 different form of the rostrum, the less elongated anterior antennae, and the very 

 different manner in which the ovisacs are borne by the female. Also in the struc- 

 ture of the natatory legs some well-marked differences are found to exist, as 

 shown in the above diagnosis. 



Occurrence. This form occurs very abundantly along the whole coast of 

 Norway, both on the outer shores and in the fjords. In the Christiania Fjord 

 I have often taken it in great numbers even close to the beach of the innermost 

 shallow creeks. As with the preceding species, male specimens are much scarcer 

 than females, and seem only to appear in certain seasons. 



Distribution. The distribution of this species seems to be very extensive. 

 It has been noted as far north as in Mosel Bay, Spitsbergen, and southwards 

 in the Mediterranean, off the Canary Islands, and even in the Indian Ocean. I have 

 myself examined specimens taken off the coast of New Zealand, and have care- 

 fully compared them with northern specimens, without having been able to 

 detect any difference whatever. 



Fam. 2. Cyclopinidae. 



Characters. Body of somewhat varying shape, but never so slender as 

 in the Oithonidce, the anterior division being, as a rule, considerably dilated. 

 Head in most cases confluent with the 1st trunk-segment; rostral projection short 

 and generally bent in against the ventral face. Anterior antennae less elongated 

 than in the Oithonidse, tapered, and clothed with moderately long seta?; those in 

 male strongly hinged. Posterior antennae generally composed of 4 joints. Oral 



2 Crustacea. 



