supplementary sensory filaments. These filaments, according to Oanu, are wholly 

 absent in the male of D. elegant. 



Occurrence. I have met with this form not (infrequently along the whole 

 Norwegian coast, from the upper part of the Christiania Fjord to Vacls0, in 

 moderate depths. All the specimens have been taken in the free state among 

 dredged material, and, though the parasitic habits of the animal are proved by 

 the structure of the oral parts, we do not as yet posess apy information as to 

 what kind of invertebrate animals are at times infested by it. 



Distribution. British Isles (Brady), Spitsbergen (G. 0. Sars). Franz 

 Joseph Land (Scott), ? Gulf of Naples (Giesbrecht). 



Gen. 20. RhyilChOmyZOn, Giesbrecht, 1895. 



Generic Characters. Body more slender than in the preceding genera, 

 with the anterior division far less expanded, and some of the trunk-segments 

 acutely produced laterally. Eostrum large and prominent, curved downwards. 

 Tail comparatively slender, consisting in female of 4, in male of 5 segments. 

 Caudal rami more or less produced. Anterior antennaB of moderate length, and 

 composed of a varying number of articulations; those in male imperfectly hinged 

 and without any supplementary sensory filaments. Posterior antenna resembling 

 in structure those in Dermatomyzon. Oral cone short and massive, not prolonged 

 in any siphonal tube. Mandibles with the masticatory part more or less cultri- 

 form; palp very small, uniarticulate. Maxillae and maxillipeds about as in Der- 

 matomyzon. Natatory legs well developed, and on the whole normally built. 

 Last pair of legs comparatively small, biarticulate, distal joint of somewhat dif- 

 ferent shape in the different species. 



Remarks. This genus, established by Giesbrecht, differs conspicuously, 

 as to the external appearance of the body, from the preceding ones, though in 

 the structural details approaching somewhat the genus Dermatomyzon. One of 

 the most conspicuous external characters is the very large and prominent falci- 

 form rostrum, which indeed has given rise to the generic name proposed by 

 Giesbrecht. The genus comprises as yet 3 well-defined species, 2 of which will 

 be described below, the 3rd species, R. falco Giesbrecht, being hitherto only 

 known from the Gulf of Naples. 



13 Crustacea. 



