8 



other oral parts, the structure of which indeed seems to be more adapted for 

 killing than for masticating the prey. 



Distribution. As this form has generally been confounded with O.plumi- 

 fera, its true distribution is as yet rather difficult to determine. In all probability 

 it has a similar wide range in the Oceans to that of the next species. With 

 full certainty it may be said to be distributed all over the North Atlantic, as 

 also in the Mediterranean. 



2. Oithona helgolandiea, Glaus. 

 (PI. in). 



Oithona helgolandiea, Claus, Die freilebenden Copepoden, p. 105, PI. XI, figs. 10 12. 

 Syn: Oithona spinifrons, Boeck. 

 pygmcea, Boeck. 

 similis, Claus. 

 spinirostris, Giesbrecht (not Claus). 



Specific Characters. Female. Body of the usual slender form, though 

 somewhat less so than in the preceding species. Rostrum, as in that species, 

 acutely pointed, but abruptly bent downwards at a right angle to the axis of 

 the body, so as not to be visible in the dorsal aspect of the animal. Genital 

 segment somewhat less dilated in its anterior part. Caudal rami not nearly 

 attaining the length of the anal segment, and less divergent than in 0. spinirostris, 

 seta of outer edge shorter. Anterior antennae, when reflexed, extending scarcely 

 beyond the anterior division of the body, and composed of about 10 joints, some 

 of which, however, are only faintly defined. Posterior antennae and oral parts 

 agreeing in structure with those in the preceding species. Natatory legs, how- 

 ever, exhibiting some characteristic differences: 1st pair with the outer ramus 

 armed in a manner similar to that in 0. spinirostris, except that the apical spine 

 is less strong and almost setiform; inner ramus apparently only biarticulate, the 

 2 outer joints being confluent. 2nd and 3rd pairs with no spine outside the middle 

 joint of the outer ramus, though exhibiting at the end of the joint a small 

 dentiform projection of the margin. 4th pair without any spines either on the 

 1st or 2nd joints. Terminal joint of this ramus in all 3 pairs with only a single 

 small spine outside, attached close to the end, and exhibiting moreover in the 

 2nd and 3rd pairs a very small dentiform prominence of the margin at about the 

 middle of the joint. Ovisacs narrow oblong and closely appressed to the sides of 

 the tail, each sac containing only a single series of very large and pellucid ova. 



Male closely resembling that of the preceding species, but of smaller size, 

 and moreover differing somewhat in the armature of the natatory legs, the ter- 

 minal joint of the outer ramus having only 2 spines outside. 



