193 



oval in outline, being slightly constricted in the middle and obtusely angular 

 in the posterior part, greatest width rather behind and not fully attaining half 

 the length, both extremities somewhat blunted at the end, the anterior narrower 

 than the posterior. Surface of valves only slightly uneven, and faintly reticu- 

 lated, being marked with somewhat irregular pittings and scattered small 

 tubercles, anterior edges and lower part of posterior armed with a very con- 

 spicuous and rather regular row of somewhat blunt denticles, but only sparingly 

 hairy. Eyes well developed. Anterior antennae with the 4 joints of the 

 terminal part well defined, last joint scarcely as long as the 2 preceding ones 

 combined. Posferior antennae moderately strong, with the flagellum quite short, 

 scarcely extending to the middle of the penultimate joint. Legs somewhat 

 less slender than in the other species. 



Male a little larger than female, and having the shell comparatively 

 narrower. Flagellum of posterior antennae more prolonged than in female, but 

 with the distal part very thin and fragile. Copulative appendages largely 

 developed and of a rather unusual shape, the basal part being produced below to 

 a greatly prominent and complicated lobe, obtuse at the end, and exerted behind 

 to a thin digitiform lappet, in front to a much stronger hooked process; ter- 

 minal part remarkably narrow and prolonged, tapering gradually to a thin 

 somewhat flexuous lash. 



Colour of shell dark yellowish brown; limbs bright yellow. 



Length of adult female slightly exceeding one millimeter. 



Remarks. In the general appearance of the shell and its sculpture this 

 form bears a rather close resemblance to the species of the preceding genus, 

 and might indeed, without a closer examination, easily to adduced to that genus. 

 Yet, the structure of the antennae and the mandibles is decidedy different and 

 proves it to be in reality referable to the genus Cythereis, as here defined. 



Occurrence. This form is by no means rare off the Norwegian coast. I 

 have taken it in many places, from the Christiania Fjord up to Finmark in 

 depths ranging from 10 to 30 fathoms, muddy bottom. 



Distribution. British Isles, Iceland, Spitzbergen, Gulf of Lawrence, Bay 

 of Biscay, Mediterranean. 



Fossil. Norway, British Isles. 



24 Crustacea. 



