Anomiidae and Mytilidae 51 



ment of the shell a notch appears in the margin of the right valve. 

 This notch IS deepened by progressive marginal growth until it 

 finally becomes an opening more or less isolated from the shell margin 

 and m position to allow passage of a byssus which becomes calcified 

 and permanently fixed. A strong muscle unites the inner surface of 

 the byssal plug with upper valve of the shell. 



Genus AiVOMIA Linne, 1758 

 Anomia*! simplex d'Orbigny PI. 6, fig. 32 



Alt. to 40; length to 44 mm. Shell fixed, inequivalve, usually 

 subcircular and conforming to the contour and sculpture of its base. 

 Structure lamellar, translucent, color golden or silvery with a lustrous 

 exterior and nacreous lining; upper valve slightly convex, interior 

 with transverse ligamentary fossette and muscle impressions. Lower 

 — right — valve flattened, with byssal sinus near apex; sinus not 

 closed at marginal border; pallial line indistinct. 



Dredged in one to six fathoms. 



Genus PODODESMUS Philippi, 1837 

 Pododesmus^'- rudis (Broderip) (P. decipiens Philippi) PI. 6, fig. 33 



Shell larger than Anomia — up to 45 mm. Inequivalve, super- 

 ior valve convex, exterior brownish, rough, with narrow, irregular 

 riblets, sometimes scaly; concentric growth lines; inferior valve 

 adapted to shape of its support; byssal sinus similar to Anomia; 

 pearly lining; one muscle scar. 



Taken with A. simplex. 



Family 3IYTILIDAE 



The Mytilidae is a large and widely distributed family, best 

 represented in cold seas, but having various genera which are adapted 

 to warmer waters. Some European members of the family rank near 

 the oysters and clams in economic importance, mussels having been 

 cultivated for food along the French and Belgian coast for several 

 centuries. All mussels are edible. They are not generally esteemed in 

 the United States as food but are much used as bait for bottom- 

 feeding fish. 



^^ Gr., anomos, without Jaw. 



*- Gr., podos, foot, desmos, ligament; rudis, rough. 



