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THE CHICAGO ACADEMY OF SCIENCES. 



Galba similis (Meek). 

 Galba diaphana (E. & S.). 

 Galba ncbrascensis (E. & S.). 

 Galba meekiana (E. & S.). 

 Galba shumardi (Meek). 

 Galba florissantica (Cockerell). 

 Galba contracosta (Cooper). 

 Galba alamosensis (Arnold). 

 Galba bonnevillensis (Call). 

 Galba bakeri (Walker). 

 Galba nashotahensis (Baker). 

 Galba accelerate (White). 



Sii'bgenus POLYRHYTIS 

 Galba kingi Meek. 



Middle Eocene. 

 Oligocene. 

 Oligocene. 

 Oligocene. 

 Oligocene. 

 Oligocene. 

 Pliocene. 

 Pliocene. 

 Pliocene. 

 Pliocene. 

 Pliocene. 

 Comanchean. 

 Meek. 



Lower Pliocene. 



II. STRATIGRAPHICAL TABLE OF EXTINCT AMERICAN LYMN^AS. 



Era. 



Mesozoic. 



Period. 



Comanchean or 

 Lower Cretaceous. 



Cretaceous. 

 Cretaceous. 



Lower Eocene. 

 Middle Eocene. 



Formation. 

 Atlantosaurus. 

 (Morrison; Como.) 



Bear River. 



Laramie. 

 f Fort Union. 

 LWasatch. 



Bridger. 



White River. 



Cenozoic. j 



-S 4 Oligocene. 



Middle Miocene. 

 Lower Pliocene. 



Upper Pliocene. 



>> 



i_i 



rt 



2 Pleistocene. 



Species. 



f ativuncvfa White. 

 { consortis White. 

 (.accelerata White. 



nitidula Meek. 

 ( tenuicosta M. & H. 

 ( t. ivhiteavesi Baker. 

 I compactilis White. 



tenuicosta M. & H. 

 i tenuicosta M. & H. 

 \ minuscula White, 

 f vetusta Meek. 

 I similis Meek. 

 (diaphana E. & S. 

 I nebrascensis E. & S. 

 1 meekiana E. & S. 



Florissant. 



Mascall. 



Humboldt. 



( Contracosta Lake bed. 

 I (Merced series.) 

 I Fernando. 



Bonneville beds. 



Anticosti Marl beds. 



Michigan Marl beds. 



Wisconsin Marl beds. 



shumardi Meek. 

 scudderi Ckll. 



sieverti Ckll. 

 ! florissantica Ckll. 

 stearnsi Hannibal. 

 kingi Meek. 



contracosta Cooper. 



alamosensis Arnold. 

 bonnevillensis Call. 

 anticostiana Dall. 

 bakeri Walker. 

 nashotahensis Baker. 



