FIG. 213. The fresh-water mussel (Unto). 



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., lateral teeth; a. a., anterior adductor 

 mark ; a.r., mark of protractor of the foot; /./., pallial line ; 

 p.a., posterior adductor mark ; p.r.^ mark of posterior retractor 

 of the foot ; Lg., a line of growth ; A., anterior (the blunter 

 nd); P., posterior; V.^ ventral. 



