123 



wise of a very similar structure. Anterior antennae shorter than in that species, 

 reaching, when reflexed, beyond the caudal rami by about the 5 outer joints. 

 Posterior antennae with the inner ramus about twice the length of the outer. 

 Oral parts and legs nearly as in the preceding species. 



Colour. Body perfectly hyaline. 



Length of adult female 3.20 mm. 



Memories. I am now of opinion that the specimen described from Nan- 

 sen's Polar Expedition as Hemicalanus spinifrons is more properly referable to 

 the above-named Mediterranean species, with which it seems to agree fairly well, 

 except in its size, which is somewhat larger. Another specimen, exactly agreeing 

 with that found in the Polar Sea, has subsequently been captured farther south, 

 in the Norwegian Sea, for which reason the species is now included in the Fauna 

 of Norway. It may be at once distinguished from H. longicornis by the spiniform 

 projection of the front, and the far less elongated anterior antennae. 



Occurrence. The above-described specimen was found in a plankton- 

 sample taken during the cruise of the "Michael Sars" in 1900 at Stat. 34, located 

 between Jan Mayen and the Norwegian coast, the depth being recorded to be 

 from 500 to 1000 metres. 



Distribution. -Mediterranean (Giesbrecht). 



Fam. 18. Arietellidae. 



Characters. Body comparatively robust, not depressed. Cephalosome, 

 as a rule, well defined from the 1st pedigerous segment, front more or less 

 produced below and carrying 2 tentacular appendages. Last 2 segments of 

 metasome united. Urosome comparatively short, composed in female of 4, in 

 male of 5 segments. Caudal rami well defined, short, with some of the apical 

 setae much elongated. Anterior antennae less slender than in the Heterorhabdidos, 

 in some cases very short, number of articulations considerably reduced, left 

 antenna, as a rule, longer than the right, and in male imperfectly geniculate, 

 with the terminal part very short, biarticulate. Posterior antennas with the inner 

 ramus longer than the outer, and having a limited number of setae at the tip. 

 Oral parts somewhat resembling in structure those in the Heterorhabdidce ; mandi- 

 bular palp, however, without any trace of an inner ramus, and posterior maxil- 



