974 



FRESH-WATER BIOLOGY 



AURICULIDAE 



^^^n^n^ 



Fig. 1. Carychium exiguum Say. 



SiPHONARIIDAE 



29 27 17 15 13 11 



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^ 



Fig. II. Siphonaria alternata Say. 



Gadiniidae 



Fig. III. Gadinia reticulata Say. 



Lymnaeidae 



(VWl^^'^ 





Fig. IV. Lymnaea stagnalis L. 



Planorbidae 



C 1-8 U 



Fig. V. Planorbis irivolvis Say. 



