. The Danish Ingolf-Expedition. Scientific expeditions; Arctic Ocean. CRUSTACEA MAI,ACOSTRACA. IV. reach that end. Telson with the proximal part of the lateral margins more convex, while these margins are about at their middle more concave than in P. typicus, according to Sars' figure; the end with 3 spines, but a smaller spine is in both specimens observed on one of the coarsely serrated lateral margins near the end. Length of the young male mm, of the female with the marsupium rudimentary mm. Remarks. By the three keels on the carapace and above all by the curious shape of the narrow
. The Danish Ingolf-Expedition. Scientific expeditions; Arctic Ocean. CRUSTACEA MAI,ACOSTRACA. IV. reach that end. Telson with the proximal part of the lateral margins more convex, while these margins are about at their middle more concave than in P. typicus, according to Sars' figure; the end with 3 spines, but a smaller spine is in both specimens observed on one of the coarsely serrated lateral margins near the end. Length of the young male mm, of the female with the marsupium rudimentary mm. Remarks. By the three keels on the carapace and above all by the curious shape of the narrow first free thoracic segment this species differs strongly from P. tvpicus. Occurrence. Not taken by the "Ingolf", but by the "Thor" at a single station. South of Iceland: Lat. 62°57'N., Long. I9°58' W., 508 fath.; 2 immature, mutilated specimens. Family Diastylidae. This large family, which is distributed all over the world, is especially represented in the arctic- subarctic and boreal regions by a large number of species; from the "Ingolf" area 19 species are dealt with in the present paper. But some questions as to the limitation of its genera are difficult; certain features fre- quently used are of slight value as generic characters. For instance, rudimentary exopods in third and fourth pairs of legs in the female are found in Leptostylis and wanting in , while in Diastvlis they are wanting in most species, but according to Caiman (1912) distinct in some forms. Whether third and fourth free thoracic segments are fused or separated is another feature used as generic character, but it has scarcely been observed that every transition between complete fusion of these segments without vestige of dorsal suture and movable articulation of these segments against one another can be pointed out; a few facts may be mentioned. Sars saj's that in Diastvlopsis resima Kr. (referred here to Brachydiastylis Stebb.) these two segments "are ve
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