54 CONCHIFERA. 



Animal compressed ; foot tongue-shaped ; siphons 

 short, separate, and diverging at the tips. 



P. rostrata. 



obtusa. Fig. 66 ; n. s. 



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. T. convexa. 



villosiuscula. distorta. 



pubescens. Fig. 68; J n. s. 



Cochlodesma (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 IV. MYAD^E. 



Shell thick, strong, opaque, gaping behind, 

 covered with a wrinkled skin (epidermis). Animal 

 with the mantle closed, giving issue to a small 

 foot ; siphons united, wholly or partly retractile ; 



