the Copepod Genus Oithona. 501 



ehort outer-edge seta ; exopodite and endopodite as in 

 0. plumifera. 



Fourth foot without an inner-edge seta on the first basal 

 joint ; an outer-edge seta on the seeond basal joint was 

 apparently absent in all the specimens examined ; exopodite 

 and endopodite as in 0. plumifera. 



Fifth foot as in 0. plumifera, 



Male unknown. 



Distribution. Common off the west and south-west coasts 

 of Ireland, 0-1000 fath. It is usually found in waters of a 

 salinity of 34*8 per mille and over, but has a few times been 

 taken in much less saline water. 



Oithona pelagica, sp, m 



Female. — Length l'36-l - 52 mm. 



Cephalothorax as in O. plumifera., the rostrum being visible 

 in dorsal view as in that species. Abdomen five-jointed, the 

 proportional lengths of the joints and the furca being 

 11:32:15:15:18: 14. 



First antenna reaching almost to the end of the body. 



Second antenna as in O. plumifera. 



Mandible as in O. plumifera, except that the endopodite 

 bears four subequal setse. 



First maxilla of the same general form as in O. plumifera ; 

 the endopodite, however, bears a medium-sized seta and the 

 second inner lobe bears a seta which reaches to the end of the 

 third inner lobe. The seta, which is situated at the base of 

 the exopodite in O. plumifera and represents the first outer 

 lobe, could not be made out, but may have been overlooked. 



Second maxilla and maxillipede as in O. plumifera. 



First foot as in O. setigera, with three outer-edge spines on 

 the third joint of the exopodite ; the outer-edge seta of the 

 second basal is, however, very slender and tapered, about 

 equal in length to the terminal spine of the exopodite. 



Second to fourth feet each with a very minute inner-edge 

 seta on the second basal. The first basal bears on its outer 

 margin a very slender tapering seta, about equal in length, in 

 the second foot, to the exopodite, but much shorter in the 

 third and fourth feet. Exopodites and endopodites as irj 

 O. plumifera. 



Fifth foot as in O. plumifera. 



Male unknown. 



Distribution. Occurs off the S.W. coast of Ireland i i » 

 waters of a salinity of 35'4 per mille and over. It has been 

 taken in nets fishing from depths of ca. 500 fathoms to the, 



Ann. & Mag. N. Hist. Ser. 8, Vol. ii. 3(j 



