FIG. 187. The Fresh-water Mussel. 



The uppermost figure represents the bivalve in motion in the mud 

 with protruded foot (F) ; note inhalant and exhalant apertures. 

 The middle figure shows the inside of the shell (left valve). The 

 lower figure shows the outside (right valve). ?<., The umbo ; 

 L., the ligament ; c.t., cardinal teeth; a. a., anterior adductor 

 mark ; a.;:, mark of anterior retractor of the foot ; /./., pallial 

 line; /.., posterior adductor mark; p.r., mark of posterior 

 retractor of the foot ; /.., a line of growth ; A, anterior (the 

 blunter end); f, posterior; I', ventral. 



