124 THE CHICAGO ACADEMY OF SCIENCES. 



Section Polyrhytis Meek. 

 Section Acella Haldeman. 

 Section Pleurolimn&a Meek. 

 Section Galba Schrank. 

 Subgenus Stagnicola Leach. 

 Section Stagnicola S. S. 

 Section Leptolimnea Swanison 

 Section Physastra Tapp-Can. 

 Genus Erinna Adams. 



In 1903 1 Dybowski proposed a classification of the fresh-water 

 pulmonates in which six families were recognized, as follows : 



Limnseidse 

 Limnophysidae 

 Amphipeplidce 

 Planorbidae 

 Ancylidse 

 Physidae 



This author thus tabulates the characters of the several groups : 

 I. Mantel mit einem iiber das Gehause aufgeschlagmen Anhange. 



1. Zahnplatten mit einem flugelartigen Anhange, alle gleichformig 



gestaltet. Family PHYSIOS. 



2. Zahnplatten ohne Anhang, der Gestalt nach drei Gruppen beldend 



Family AMPHIPEPLIDCE. 

 II. Mantel normal, ohne Anhange. 



1. Gehause in die Lange gestrickt. 



(a) Letzter Umgang sehr gross, bauchig aufgetrieben ; Schale 

 unregemassig quergestreift ; Glasur weisslich ; Lippe f ehlt. 



Family LIMN^ID^E. 



(b) Letzter Umgang ausgezogen, wenig gewolbt; Schale sehr 



f ein und ziertich langs und quergestreift ; Glasur 

 rotlich; Lippe rotbraun. Family LIMNOPHYSID.E. 



2. Gehause in die Quere gestrickt. 



(a) Gehause scheibenformig. Family PLANORBID^:. 



(b) Gehause mutzenformig. Family ANCYLID^E. 

 In the above classification only the shell, mantle and radula are 



used as diagnostic factors. It is probable, however, that a study of 

 the genitalia, nervous system and pallial organs will bear out the 

 grouping substantially as proposed by Dybowski. The separation of 

 Limnophysa from Lymnseidae as a family is, however, not borne out 

 by present studies, there being no distinguishing features by which 

 the group can be separated from the other Limnseidse, except as a 

 genus. 



In the present monograph it is proposed to classify the Lym- 

 naeids by the characters of the shell, genitalia (shape of prostate, rela- 

 tive size and form of penis and penis-sac) and radula. The study of 



l Nach. Deutsch. Mai. Ges., XXXV, pp. 130-144. 



