MACTRA KNEADING-TROUGH. 165 



grey, 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, 

 roundish, compressed, thin, semipellucid, finely 

 striated ; umbones small, central ; hinge without 

 lateral teeth, cartilage cavity large, triangular, 

 cardinal teeth small, a single one locking into a 

 bifid one in the opposite valve ; of a yellowish, 

 reddish, or white colour often stained with black 

 occasioned by the mud in which it resides ; 

 about an inch and quarter long, and an inch 

 and half broad. 



This is one of the most beautiful of the Bri- 

 tish species of Mactra ; it is chiefly found at the 

 mouth of inlets or rivers, not remote from fresh 

 water ; for though it always seeks a spot within 

 reach of the flux of the tide, it delights in situa- 

 tions over which fresh water occasionally flows. 

 It lives in the mud, buried about five or six inches 

 deep. The animal has two slender tubes of a 

 yellowish colour placed near together at the an~ 

 terior end of the shell : one about three inches 



