TUP: L\\ii:i,uim.\M m 



407 



face is usually mark.-d l>y <-<>nrrnt ri.- ///// N <>f ,/r<rf/ t . which 

 indicate the boundaries of the successively added new layers 

 of shell-substance. 



Pro. 117. Sectional diagram of a fresh-water Mussel (Anodonta). A, 4. mantle, the 

 light, lobo of which is cut away; B, foot ; C, branchial chamber of the mantle 

 cavitv ; D. unal chamber; 7, anterior adductor muscle; 77, posterior adductor 

 muscle; 777. retractor muscle of the foot; a, mouth; b, stomach; r. intestine, 

 the turns of which are supposed to be seen through the side-wall? of the tnr-in- 

 soma; d. rectnm: e. anu^: /', ventricle; (7, auricle; />, L'ills, except /. right exter- 

 nal ill. larirdy cut away and turned back; A', labial palpi; /, cerebral; m, pedal; 

 n, parieto-splanchnic ganglia; 0, aperture of the kidney or organ of Bojanue; p, 

 pericardium. 



The applied edges of the two valves are very often pro- 

 duced into elevations and depressions which interlock with 

 one another. The form and arrangement of these teeth and 

 sockets are of much use in systematic conchology. 



