124 l HI. CHICAGO ACADEMY OF SCIENCES. 



Section Polyrhytis Meek. 

 Section Acclla Haldeman. 

 Section Pleurulinincca Meek. 

 Section Galba Schrank. 

 Subgenus Stagnicola Leach. 

 Section Stagnicola S. S. 

 Section Leptolimnea Swanison 

 Section Physastra Tapp-Can. 

 Genus Eriima Adams. 

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

 pulmonates in which six families were recognized, as follows : 



Limnseidae 

 Limnophysidse 

 Amphipeplidse 

 Planorbidse 

 Ancylidae 

 Physidse 

 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 Physid.e. 



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



Family Amphipeplid.e. 

 II. Mantel normal, ohne Anhange. 



1. Gehause in die Lange gestrickt. 



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

 unregemassig quergestreift ; Glasur weisslich; Lippe fehlt. 



Family Limx.eid.e. 



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



fein und ziertich langs und quergestreift; Glasur 

 rotlich ; Lippe rotbraun. Family Limnophysid.e. 



2. Gehause in die Quere gestrickt. 



(a) Gehause scheibenformig. Family Planorbid.e. 



(b) Gehause mutzenformig. Family Axcylid.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 Limnaeidae, 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 



iNach. Deutsch. Mai. Ges., XXXV, pp. 130-144. 



