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DIVISION IV. Shell oblong, gibbous, with the posterior side dilated and 

 elevated above the hinge, apex rounded. 



Scientific name. Locality. Scientific name. Locality. 



Modiolus, Brit. W. Indies, Africa. 



DIVISION V. Only found in fresh water. 



Cygneus, Europe. Fucatus, Wiltshire, N. America. 



Fkiviatilis, North America. Dubius, Senegal, China. 



Stagnalis, Lake of Schwanzee. Americanus, North America. 



Anatinus, Europe. 



DIVISION VI. Eared. 



Family 1st. Valves rather compressed. 



Margaratiferus, Amboyna, China. Unguis, Mediterranean. 



Radiatus, Tranquebar. 



Family 2cL Willi one valve more convex than the other. 



Hirundo, West Indies, Ceylon, Moria, Red Sea. 



Mausilius, Britain. Ala Corva, South Seas. 



DIVISION VII. Shell suborbicular, longitudinally striated, and margin 



crenulated. 



Faba, Greenland. 



DIVISION VIII. Somewhat tongue-shaped, apices acute. 

 Lingua, Amboyna. Camella, Japan. 



