1870.] BRADY— ON BIVALVE CRUSTACEANS. 381 



median sinuation. Seea from above, the outline is broadly 

 ovate (almost elliptical), only slightly narrower in front than 

 behind ; greatest width equal to the height, and situated near 

 the middle : extremities broadly and evenly rounded. Hinge- 

 margins somewhat depressed; hinge-processes strongly developed. 

 Surface of the shell smooth and polished, beset with n.ore or 

 less numerous circular punctures, each bearing a short rigid 

 hair. Colour yellowish white. Length --h inch. 



This is the most abundant species in the dredgings here des- 

 cribed, and occurs in greater or less quantity in almost all the 

 localities. In Britain it is known only from the single (?) speci- 

 men described by Mr. Norman, which was taken in *' very deep 

 water " in Unst Haaf. Mr. Norman's description applies accur- 

 ately to the American specimens, except in the matter of the 

 "distant punctured papillse." The ornamentation, it is true, 

 does appear papillose in some lights ; but this is, I think, an 

 optical illusion : when carefully examined, the seemingly elevated 

 circles resolve themselves into concave pits, each with a little 

 central bristle. I have seen a single fossil valve of this species 

 from the Scottish glacial clay. 



Cythere tuherculata, Sars. 



These specimens are much less rounded in outline and more 

 rugged in general appearance than is usual with European speci- 

 mens ; there is also a tendency, more or less pronounced, to the 

 formation of one or more longitudinal ridges near the ventral 

 border. But the distinctions do not seem sufficient to warrant 

 the separation of the form as a new species. 



Cythere Canadensis^ nov. sp., figs. 4-6. 



Carapace elongate, compressed ; seen from the side, quadrate ; 

 greatest height situate at the anterior third, and scarcely equal 

 to half the length ; anterior extremity very obliquely rounded, 

 and bordered at the lower angle with several small teeth ; pos- 

 terior subtruncate, slightly emarginate in the middle ; superior 

 margin gently sloping, nearly straight, sinuated behind the 

 anterior hinge ; inferior margin also straight, excepting a slight 

 median sinuation. Seen from above, somewhat lozenge-shaped, 

 somewhat tapered toward the front, more rounded behind 

 widest near the middle : width equal to about two-fifths of the 

 length; extremities obtuse, subtruncate. Shell-surface uneven, 

 Vol. V. A* No. 4. 



