147 



among algae. On the other hand, I have never met with it in any of the numer- 

 ous plankton-samples examined by me, for which reason I have come to the con- 

 clusion that, at any rate off the Norwegian coast, this Calanoid is a strictly 

 littoral form. It moves in the usual manner, now proceeding rather slowly in a 

 somewhat jumping manner by rhythmical strokes of the posterior antennae and 

 mandibular palps, now starting away more suddenly by employing the natatory 

 legs and the urosome. 



Distribution. British Isles (Brady), coast of France (Canu), Mediterranean 

 (Giesbrecht). Atlantic Ocean between 50 and 59 N. Lat. (Giesbrecht). 



Fam. 23. Acartiidae. 



Characters. Body more or less slender, with the anterior division but 

 slightly vaulted. Cephalosome well defined from the 1st pedigerous segment; 

 front without any rostrum. Last 2 segments of metasome united. Urosome con- 

 sisting in female of 3, in male of 5 segments. Caudal rami with the full number 

 of setoe. A single eye present. Anterior antennae very slightly attenuated and of 

 a peculiar nodular appearance, the articulations being rather irregular and some- 

 times indistinctly defined, bristles very unequal; right antenna in male slightly 

 transformed, and imperfectly geniculate. Posterior antennae very delicate, with 

 the inner ramus very slender, outer poorly developed. Oral parts conspicuously 

 differing from those in other Calanoids ; posterior maxillipeds, however, built upon 

 a somewhat similar type to that in the Pontellidce. The 4 anterior pairs of legs 

 very slender and delicate, with unusually long natatory setae; inner ramus in all 

 these pairs biarticulate. Last pair of legs not natatory, uniramous in both sexes, 

 very small in female, somewhat larger and subprehensile in male. No ovisac 

 present in female. 



EemarTcs. This family is established to include the genus Acartia of 

 Dana, which in several respects differs materially from the other known Calanoida, 

 representing quite a particular type. It is only in the structure of the maxillipeds 

 that some agreement is found to the Pontellidce, to which family this genus has 

 often been referred ; but otherwise it is widely different. In addition to the typi- 

 cal genus, another nearly-allied genus has recently been established by Th. Scott 

 as Paracartia. Only the former genus is represented in the northern seas. 



