MACTRA PEPPER MACTRA. 161 



and do not display much beauty ; they are usually 

 semipellucid, and of a thin delicate appearance ; 

 the surface is seldom diversified by inequalities. 

 The prevailing colour is blueish, or yellowish 

 white, sometimes radiated. The animal has 

 not the power of progressive motion, but by the 

 assistance of a small compressed muscular foot, 

 is enabled to change his position a little : this 

 organ projects at one end of the shell, and at the 

 other are two tubes formed by the mantle. The 

 name Mactra is derived from the Greek /xarpa 

 (mactra a kneading-trough. 



MAGTRA Stultorum.* 



SIMPLETON'S KNEADING-TROUGH. 



Specific character. Shell subtriangular, con- 

 vex, thin, brittle, semipellucid; colour white gray, 

 or pale brown, radiate more or less from the 

 hinge with paler stripes, sometimes of a purplish 

 hue about the beaks, and inside of the valves ; 

 the umbones are gibbous ; length an inch and 

 a quarter, the breadth one and three quarters. 

 Common on most sandy coasts. 



MACTRA Compressa, or Piperata. 

 PEPPER MACTRA. 



Specific character. Shell subtriangular, roun- 

 dish, compressed, thin, semipellucid, finely stri- 



t Plate VIII. figure 4. 



14* 



