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the length, dorsal margin rather bowed in the ocular region, but sloping 

 evenly behind, ventral margin slightly sinuated in front of the middle, anterior 

 extremity obliquely rounded and somewhat bowed below, posterior produced 

 in the middle to an obtuse prominence not clearly defined below; seen dor- 

 sally, broadly ovate in outline, with the greatest width behind the middle and 

 about equal to the height, side-edges iregularly bent posteriorly, anterior 

 extremity evenly tapered, posterior somewhat abruptly contracted at the end 

 to a conical prominence. Valves with the alaeform expansions well marked, 

 but not much prominent, terminating behind in an obtuse angle, surface marked 

 with slight pittings arranged in more or less vertical rows. Antennae moderately 

 slender, the anterior ones with the penultimate joint about twice as long as 

 the preceding one. Legs gradually increasing in length posteriorly, last pair 

 with the 1st joint of the terminal part considerably longer than the other 

 2 combined. 



Male a little smaller than female, but only slightly differing in the shape 

 of the shell. Copulative appendages of moderate size, with the basal part 

 rounded triangular in shape, foremost corniform proces tripartite at the ex- 

 tremity; terminal part rather narrow and transversely truncated at the end. 



Colour of shell whitish gray, semipellucid. 



Length of adult female 0.65 mm. 



Remarks. This form was recorded in the year 1865 by Norman as a 

 species of Cythere, and was in the same year observed by the present author, 

 but erroneously identified with Cylhere convexa Baird, which is a true member 

 of the genus Hemicythere, as defined above. In the general outward appear- 

 ance it is not unlike some of the species of the genus Loxoconcha, and may 

 easily, at the first sight, be mistaken as such. On a closer examination it is 

 however found to differ essentially in the absolute want of eyes and in the 

 presence of distinct, though rather small alaeform lateral expansions of the 

 valves. The structure of the limbs and of the copulative appendages in the 

 male moreover proves it to be a genuine membre of the present genus. 



Occurrence. I have taken this form not unfrequently in the upper part of 

 the Christiania Fjord, as also in several other places on our coast up 

 Finmark, at depths ranging from 10 to 30 fathoms muddy bottom. 



Distribution. British Isles, Holland, Iceland, Spitzbergen, Baffins Bay. 



Fossil. Norway, Scotland, Canada. 



