42 



ERYCINA. 



E. cequorea. Shell subtriangular, equilateral, thick ; umbonial 

 slope angulated and submarginal ; umbo a little flattened, apex 

 acute; hinge callous; cardinal and lateral teeth compressed and 

 prominent ; fosset oblique, obovate ; lunule large, elliptical, de- 

 fined by an impressed line. 



E. rectilinear is. Shell subtriangular, compressed : subequilate- 

 ral : anterior and posterior margins nearly rectilinear from the 

 apex, which is acute ; umbo fluttered : beaks prominent ; luuule 

 elliptical, not well defined ; a slightly impressed line extends 

 from the anterior end towards the apex. 



MACTRA. 



M. ilecisft. Shell subtriangular. inflated, thin : posterior side 

 short and flattened : umbonial slope angulated ; a few promi- 

 nent acute lines on the posterior depression ; fosset oblique, obo- 

 vate, lateral teeth compressed and much elevated ; cavity very 

 capacious. 



M. /*M,'/r*MM/s.. Shell subtriangular compassed, equilateral, 

 thin and fragile; umbonial slope suhmarginal, nearly recti- 

 linear, carinatcd : beaks slightly prominent ; lunule narrow 

 elliptical : two slightly prominent lines behind the umbonial 

 slope. 



M, panlis. Shell triangular, equilateral, smooth and polished ; 

 both ends depressed and striated ; lunule none ; cavity capacious. 



DONAX. 



' .D. limatnla. Shell subtriangular, with obscure radiating striae ; 

 posterior side produced and cuneiform; rounded at the end; 

 dorsal margin subrecti linear: beaks prominent pointed; lunule 

 very small, marked by a profound groove ; margin minutely 

 crenulated ; cavity moderately capacious. 



AMPHIDESMA. 



A. linosa. Shell longitudinally subovate, with fine concentric 

 raised stria?; posterior side short, folded, subtruncated at tho 

 end; beaks slightly prominent ; cardinal and lateral teeth com- 

 pressed ; fosset narrow-elliptical, elongated ; cavity not capa- 

 cious. 



PSAMMOBIA. 



P. filosa. Shell elongated, with concentric acute stria3, very 

 prominent on the smaller side, which is narrowed 'and subangu- 

 lated at the end ; beaks not prominent anterior dorsal margin 

 straight, and the end obtusely rounded ; basal margin straight. 



P. eborea. Shell oblong-oval, cojnpressed ; posterior side 

 longest and obliquely truncated at the end; dorsal margin 

 straight ; beaks slightly prominent. 



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