104 



Diatrihution. — Arctic Ocean, widely distributed: Greenland, Spitsber- 

 gen, Franz Josephs Land, the Kara Sea, the Sibirian Polar Sea, oiF Jan 

 Mayen (Norw. North Atlantic Expedition). 



Gen. 2(3. OnesimuS, Boeck, 1870. 



Body rather thickset, with the coxal plates of moderate size, and the 

 last pair of epimeral plates of metasome distinctly produced at the lateral 

 corners. Antennae in female not very slender, the inferior ones generally a 

 little longer than the superior; in male considerably more elongate and both 

 provided with distinct calceolse. Epistome not ^•ery projecting, though defined 

 from the anterior lip by a distinct sinus. Posterior lip membranous, each 

 lobe having at the end exteriorly a small denticle. Mandibles rather strong, 

 molar expansion short and thick, nearly transversely truncated' at the tip, 

 pal]) scarcely longer than the mandible and originating at about the same 

 level as the latter. Maxillae nearly as in Alibrotus. Maxillipeds less strong, 

 masticatory lobe reaching to the end of the antepenultimate joint of the 

 palp, the lattei' not nearly so robust as in the said genus and attenuated 

 distally. Anterior gnathopoda of moderate size, distinctly subchelifonn. Post- 

 erior gnathopoda about as in Alibrotus. Pereiopoda rather short and robust, 

 the 3 posterior pairs sometimes very stout, with the joints laminarly expanded. 

 Last pair of uropoda very short, scarcely reaching beyond the preceding pair, 

 rami without any marginal setae. Telson short and Ijroad, more or less dis- 

 tinctly incised posteriorly. 



RemarJis. — In the restriction here adopted this genus is chiefly dis- 

 tinguished from the i)receding one by the much more robust form of the 

 body, by the shorter and stouter antennae and legs, as also by the poor 

 development of the last pair of uropoda. The genus would seem to be 

 chiefly confined to the Arctic seas and contains several .s^oecies, some of 

 which are, however, as yet imperfectly known. Besides the 3 Norwegian 

 forms described in the sequal, two new species, 0. turgidus and 0. leucopis 

 were procured on the Norwegian North Atlantic Exj^edition, and Dr. Hansen 

 has added 3 new species from the Kara Sea, viz., 0. caricus, breiicaicdatus and 

 affinii. Finally Dr. Stuxberg enumerates 3 sjiecies from the Siberian Polar 

 Sea, viz., 0. zehra, vorax, and ahi/^^icohi, without however giving any description 



or figure. 



