LYMNAIDZ 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 Lymnzid 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 LYMNZAEAS. 
Family LYMNAID Keferstein. 
Genus LYMNA&A Lamarck. 
Lymnea stearnst Hannibal. Middle Miocene. 
Genus PLEUROLIMN/EA Meek. 
Pleurolimnea tenuicosta (M. & H.). Cretaceous. 
Pleurolimnea tenuicosta 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 (Meck). Middle Eocene. 
