238 



obliquely ascending behind, anterior extremity bluntly rounded off, posterior 

 drawn out quite above to a rather prominent obtuse protuberance; seen 

 dorsally, very broad, square-shaped, with the greatest width, between the tips 

 of the lateral expansions, about equal to 2 /s of the length, side-edges angularly 

 bent behind the middle, anterior extremity obtusely pointed, posterior abruptly 

 contacted to a narrow conical prominence. Valves rather thin, with the sur- 

 face slightly rugulose and marked with distant small pits, posterior edges finely 

 denticulate, lateral expansions very prominent, alaeform, and almost rectangular 

 in shape, each terminating in an obtusely rounded corner and having moreover 

 traces of 2 or 3 blunt prominences of the hind margin. Eyes absent. Struc- 

 ture of the limbs quite normal. 



Male somewhat smaller than female, and having the shell comparatively 

 narrower, as seen laterally. Copulative appendages with the terminal part oval 

 in shape, and having attached to its base in front a peculiar somewhat twisted 

 deflexed lobule. 



Colour of shell whitish pellucid. 



Length of adult female 0.70 mm. 



Remarks. In the outward appearance this form looks rather different from 

 the other known species, and bears a perplexing similarity to some of the 

 species of the genus Cytheropteron. The structure of the several limbs proves 

 it however to be a true member of the present genus, being apparently nearly 

 allied to B. dromedaria. 



Occurrence. I have hitherto only met with this species off the Lofoten 

 islands, where 2 specimens, male and female, were taken in the considerable 

 depth of 120 fathoms, soft clay. 



Distribution. As yet not recorded out of Norway. 



Gen. 46. Pseudocythere, G. O. Sars, 1865. 



Generic Characters. Shell much compressed, without any lateral ex- 

 pansions; posterior extremity produced above to a caudiform prominence. 

 Surface of valves quite smooth, without any obvious sculpture, inner duplicatures 

 rather broad, marginal zone well marked and crossed by distant pore-channels; 

 hinge imperfect. Eyes wholly absent. Anterior antennae with the terminal 

 part distincly 5-articulate, the 4 proximal joints rather short and stout, last 

 joint abruptly much narrower and greatly prolonged, setae of this part unusu- 

 ally long and slender, forming together a dense apical fascicle. Posterior 



