Shell s;:'iall , thin, transversely elonga^-e, widest at about 

 the middle of the shell; umbones i.^flated, almost terminal; um- 

 bonal ridge strong, but rounded, becoming lower and broader post- 

 eriorly; prosiimal third or more of the dorsal margin straight, 

 forming a subrounded angle of cbout 140° with the distal portion, 

 vrhich is gently curve'' or slightly emar^inated; ventral marp,-in 



usually slightl., concave; posterior margin narrow, abruptly round- 

 ed; external surface sculptured v/ith numerous, inconspicuous, round- 

 e'"i radial ribs, separated by interspaces of the same ?;iclth or nar- 

 rower; r'-rdials usually obsolete on the most convex portion of the um- 

 bonal ridge; co-centric sculpture of usually faint incremental lines, 



occasionally e^ ag.n-e rated; hinge often with sugp-est iont. of denti- 

 tion, with two or three projections on the left valve and obscure 

 sockets on the left; oroxir-al portion of the inner dorsal Diarsin con- 

 spicuously.' crenulated, the distal portion weakly crenulate^. and 

 the remainder of the marp-in usually axiooth or very feebly crenulat- 

 ed. 



I>imensions .- Max. lat. ( do rso- ventral) 5.5 j;im. ; alt. (antero- 

 posterior) 10.5 mm.; semidiam., 1.8 mm, 



5emar-:s .- l^his solitary member of the gcmzs is well represent- 

 ed in the material at hand. i^he width varies eo ns iderabl; , the 

 valve measured being the widest. The angle between the two portions 

 of the posterior margin is not sharp, but rou::ded or siibrouiided. 

 A rather sur-orising feature is t?ie indication of hinge dentition 



