198 



MOLLUSCA. LAMELLIBRANCH1A 



or ploughshare-shaped, and is used for crawling, or for 

 burrowing in sand or mud. Sometimes, as in the case of 

 Trigonia, by means of a rapid movement it enables the 



Fig. 91. Mya arenaria. The left valve and mantle and half the siphons 

 have been removed, a, anterior adductor muscle ; a', posterior 

 adductor ; b, visceral mass ; c, cloacal chamber into which the anus 

 opens; /, foot; g, branchiae ; It, heart; m, cut edge of the mantle; 

 o, mouth ; p, edge of mantle ; s, branchial siphon ; s', anal siphon ; 

 t, labial palps ; v, anus. (From Woodward.) 



