54 



CONCHIFERA. 



Animal compressed ; foot tongue-sliaped ; siphons 

 short, separate, and diverging at the tips. 



P. rostrata. 



obtusa. Fig. 66 ; ;^. s. 



69 



T. convexa. 

 distorta. 



Lyonsia (Turton). Shell convex on both sides : 

 hinge toothless, but furnished with a moveable 

 shelly piece, connected with each valve. 



L. Norvegica. Fig. 67 ; ^ n. s. 



Thracia (Leach). Shell transversely ovate, 

 thin, unequal- valved, nearly equal-sided ; hinge a 

 thickened shelly fulcrum in each valve ; ligament 

 partly internal ; beaks entire. Animal — siphons 

 long, entirely separated. 



T. phaseolina. 

 villosiiiscula. 

 pubescens. Fig. 68; ^ 



Coclilodesma (Couthouy). As Thracia^ but the 

 hinge a spoon-shaped horizontal process in each 

 valve ; ligament external, slight ; beaks fissured. 



C. prsetenue. Fig. 69 ; n. s. 



Family IY. Myad^. 



Shell thick, strong, opaque, gaping behind, 

 covered with a wrinkled skin {epidermis). Animal 

 with the mantle closed, giving issue to a smaii 

 foot ; siphons united, wholly or partly retractile ; 



' • TT" / ' • t> • 



