448 CYPRINID^. 



ish flesh-colour. The variety of painting is indeed great ; 

 one of the prettiest consists of a delicate network of bi'own 

 lines upon a white ground. The ventral margin which 

 rises much more behind, where it slopes uninterruptedly 

 without angulation to the dorsal edge (with which it 

 forms a more or less distinct angle), is not particularly 

 arcuated in the middle. Both dorsal margins are elongated, 

 the front one, which is always the more sloping, is straight, 

 the hinder one barely convex ; in extent of declination 

 they vary much, but always observe their relative propor- 

 tion, the front slope being sometimes abrupt, and the hinder 

 very decided, in which case the contour is almost trian- 

 gular ; when, on the contrary, the front slope is only mo- 

 derate, and the hinder one rather slight, the contour then 

 approaches a rounded oval. The anterior side, which 

 although the shorter is often not greatly so, is subangulated 

 below, the angle being rounded off; the most projecting 

 part of the hinder termination is above the middle. The 

 umbones are prominent, and lean a little forward ; the 

 beaks, which are very acute and obliquely inflected, are 

 preceded by a large lunule of an elongated heartshape, 

 which is not sunken, but defined by a groove. The hinder 

 dorsal area is neither peculiarly flattened nor excavated ; 

 the ligament is either totally concealed or linear and sunken. 

 The interior is white, or tinged with flesh colour on the 

 disk, but never stained with any dark colour upon the 

 hinder side or upon the hinge margin. The hinge is fur- 

 nished in the left valve with a rather large approximate 

 front lateral lamina, and three divergent primary teeth, 

 of which the anterior one is bifid ; in the right valve 

 with three primary ones, the central of which is very in- 

 distinctly cloven, and a tooth-like receptacle for the oppo- 

 site lamina. The inner margin is quite entire. 



