21 L 



the basal one. 1st pair of legs with the outer ranius much shorter than the 

 inner, though extending about as far as the 1st joint of the latter, middle joint 

 provided inside with a small seta; inner ramus distinctly 3-articulate, 1st joint 

 with the seta of the inner edge attached near the end, the last 2 joints combined 

 considerably exceeding half the length of the 1st. Natatory legs of the structure 

 characteristic of the genus. Last pair of legs with the distal joint very small, 

 inner expansion of proximal joint much produced, linguiform, and provided with 

 6 marginal seta?, one of which is much elongated. Ovisac of moderate size, oval 

 in forme. 



Colour, according to Prof. Lilljeborg, greyish white. 



Length of adult female 0.50 mm. 



Remarks. This form, first described by Th. Scott as a species of the 

 genus Canthocamptus, is unquestionably congeneric with the 2 preceding species, 

 exhibiting, as it does, all essential characters of the gen. Mesochra. According 

 to Th. Scott, the form recorded some years later by Prof. Lilljeborg as Cantho- 

 camptus megalops is identical with the present species. It is easily recognised 

 by its comparatively short depressed body and by the structure of the 1st pair 

 of legs, the inner ramus of which has the 2 outer joints considerably more fully 

 developed than in the 2 other species. 



Occurrence. I have only met with this form in a single locality, viz., in 

 a brackish tarn off the sout coast of Norway, "Ostravigtjernet", in which arti- 

 ficial cultivation of oysters was for the first time established by the late Prof. H. 

 Rasch. It occurred here only quite occasionally. Only female specimens were found. 



Distribution. Scottish coast (Scott), Baltic coast of Sweden (Lilljeborg). 



Gen. 46. NitOCra, Boeck, 1865. 



Generic Characters. Body of slender cylindric form, resembling somewhat 

 that in the genus Canthocamptus. Segments of urosome coarsely spinulose at the 

 hind edge ventrally and laterally, last segment exhibiting also a dorsal series of 

 spinules, anal opercle regularly denticulated at the edge. Caudal rami short, 

 more or less covered with spinules in addition to the usual seta?. Rostral pro- 

 jection very small, narrow conical in form. Anterior antenna? of moderate size, 

 8-articulate, and densely fringed with slender bristles; those in male transformed 

 in the usual manner. Posterior antenna? with the basal part distinctly subdivided, 



