LYMN^EIDyE OF NORTH AMERICA. 85 



presented itself. An endeavor has been made in Table I to place the 

 extinct species in their proper genus or subordinate group. This has 

 been difficult in many cases because of the necessary lack of anatomical 

 details, upon which data the classification of the recent species is based. 

 It is thought that the result may not be without value from a taxonomic 

 point of view. It will be noted that nearly all of the groups of the 

 recent species are represented. 



Table II illustrates the stratigraphical relations of the various 

 species. It will be noted that the number for the entire series from 

 Cretaceous to Pleistocene is but twenty-five; adding the six 

 undetermined species, we have a grand total of thirty-one species. 

 Comparing the faunas of the successive formations, it will be apparent 

 at once that the Lymnaeid fauna, as shown by the records, has been 

 neither abundant nor diversified as compared with that of the present 

 time. This may be, and probably is, due to lack of extended exploration 

 in the localities in which the strata occur. The largest number of 

 species is from the White River beds of the Oligocene, in which four 

 species have been found. Future research will doubtless extend our 

 knowledge of the fresh-water Pulmonata to such a degree that a con- 

 tinuous record will be established from the earliest period of appear- 

 ance to the present time. The hope is also entertained that the history 

 of the family may be carried back to Paleozoic strata and that data 

 may be secured bearing on the origin of this family from some marine 

 or brackish water form. 



I. SYSTEMATIC TABLE OF EXTINCT AMERICAN LYMN^EAS. 



Family LYMNJEID.E Keferstein. 



Genus LYMNiEA Lamarck. 



Lymncca steamsi Hannibal. Middle Miocene. 



Genus PLEUROLIMN^A Meek. 

 Pleurolimncea tcnuicosta (M. & H.). Cretaceous. 



Pleurolimnaa tcnuicosta whiteavesi Baker. Cretaceous. 



Genus GALBA SCHRANK. 

 Subgenus GALBA (typical). 

 Galba ativuncula (White). Comanchean. 



Galba nitidula (Meek). Cretaceous. 



Galba minuscula (White). Lower Eocene. 



Galba scudderi (Cockerell). Oligocene. 



Galba sieverti (Cockerell). Oligocene. 



Galba anticostiana (Dall). Pleistocene. 



Subgenus STAGNICOLA Leach. 

 Galba compactilis (Meek). Cretaceous. 



Galba consortis (White). Comanchean. 



Galba vetusta (Meek). Middle Eocene. 



