INTRODUCTION. 55 
GEN. 11. Ostrea.—Animaltethys ; tes- 
ta bivalvis, inæquivalvis, sub au- 
rita ; cardo edentulus, fossula cava, 
ovata, striisque lateralibus transver- 
sis; vulva anusve nullus. 
GEN. 12. Anomia.—Animal corpus li- 
gula emarginata, ciliata, ciliis val- 
vulæ superiori affixis, brachiis duo- 
buslinearibus, corpore longioribus, 
conniventibus, porrectis, valvulæ 
alternis , utrinque ciliatis, ciliis af- 
fixis valvulis utrisque. 
Testa inæquivalvis, valvula alte- 
ra planiuscula, altera basi magis 
gibba , harum altera sæpè basi per- 
forata; cardo edentulus cicatricula 
lineari prominente introrsum dente 
laterali, valvulæ vero planioris in 
ipso margine; radii duo ossei pro 
basi animalis. 
GEN. 19. Mytilus. — Animal ascidia ; 
testa bivalvis, rudis, sæpius aflixa 
bysso; cardo edentulus, distinctus 
