255 



arched throughout, ventral almost straight, anterior extremity narrowly pro- 

 duced, posterior somewhat broader and obliquely rounded off; seen dorsally, 

 very narrow, oblong in outline, with the side-edges almost straight in the 

 middle and both extremities obtusely pointed. Valves less transparent than in 

 C. vitrea, but with the surface perfectly smooth and polished. Eye well 

 observable in the living animal. Anterior antennae comparatively less slender 

 than in the said species, but of a rather similar structure, though the mutual 

 relation of the joints is a little different. Posterior antennae with the dividing 

 suture of penultimate joint located near the extremity, apical claw rather slender. 

 Legs rapidly increasing in length posteriorly, last pair considerably more strongly 

 built than the other 2, with the joints of the terminal part distinctly ciliated 

 along the anterior edge. 



Male, unlike the case with the 2 preceding species, of smaller size than 

 female, and very little differing in the shape of the shell. Copulative appen- 

 dages with a rather conspicuous thickish curved prominence in front; terminal 

 part very small, irregularly oval in shape, and pointing straight downwards. 



Remarks. In the general shape of the shell this form bears some 

 resemblance to C. vitrea; but the structure of the several appendages seems 

 to be more in accordance with that in C. Fischeri. It is however of much 

 smaller size than either of these 2 species, and differs also conspicuously 

 in colour. 



Occurrence.-- Several specimens of this small species were collected, many 

 years ago, at Skutesnaes, southwest coast of Norway, in rather shallow water 

 among algae, and I have also met with it occasionally in some other places 

 on our coast. 



Distribution. -As yet only known from Norway. 



Gen. 52. Paradoxostoma, Fischer, 1855. 



Generic Characters. Shell thin and fragile, of somewhat different shape 

 in the several species, but, as a rule, higher behind than in front, inner 

 duplicatures of valves less broad than in the preceding genera, marginal zone 

 very narrow, with only slight traces of pore-channels. A single well-developed 

 eye present. Anterior antennae slender and narrow, but with the distal segment 

 of the basal part less prolonged than in the 2 preceding genera ; terminal'part 

 composed of 4 well defined joints clothed with scattered rather short setae, the 

 last 2 joints much smaller than the preceding ones. Posterior antennae with 

 the penultimate joint distinctly subdivided and provided in front with a small 



