Posterior ridge sharp; lunule narrow; central and east-central states 117. 



117. With a radial depression before the posterior ridge; with a few radial 



lines on a flat posterior slope 



Truncilla truncata Raf. Deer-toe 

 No radial depression before the posterior ridge; with many fine radial 

 lines on a flattened posterior slope 



Dysnom\a triquetra (Raf.) 



118. Shell and hinge line thick and heavy; Mississippi River 



Lampsilis higginsii (Lea) Higgin's Eye 

 Shell and hinge moderate to thin 119. 



119. Posterior ridge very sharp and posterior slope flat, so that the shell looks 



as if it had been sliced off posteriorly; Ohio River drainage 

 Lampsilis ovata (Say) Ohio Pocketbook, Grandma 

 Posterior ridge moderate or absent 120. 



120. Shell evenly marked with many fine wavy rays; small, seldom over three 



inches; Ohio River drainage 



Lampsilis fasaola Raf. Wavy-lined Pocketbook 

 (Ligumia fasciola (Raf.)) 

 (Lavipsihs miduradiata (Lea)) 

 Rays usually irregularly distributed and of varying widths; becoming 

 larger 121. 



121. With a moderate posterior ridge; nacre tinged with red or purple; At- 



lantic drainage only 



Lampsihs ochracea (Say) Red-lined Pocketbook 

 Posterior ridge not well marked; nacre white or pinkish; Atlantic and 

 Mississippi drainages 122. 



122. Cardinals of right valve long and thin, resembling the laterals; epidermis 



smoky, scarcely rayed; shell thin and very much inflated; southern 

 Mississippi drainage 



Proptera capax (Green) Fat Pocketbook 

 Cardinals tooth-like, rather than knife-like; epidermis yellow, usually 

 rayed 123. 



123. Rays largely confined to the posterior slope; Atlantic drainage 



Lampsilis cariosa (Say) Eastern Pocketbook 

 Rays usually scattered; Mississippi drainage 



Lampsilis cardium Raf. Common Pocketbook 

 Lampsilis ventricosa (Barnes) 



Baker, F. C. 1911. The Lymnaeidae of North and Middle America. Chicago 

 Academy of Science. Special Publication No. 3 



Baker, F. C. 1928. The Fresh-water Mollusca of Wisconsin. Two vols. Wis- 

 consin Geol. and Nat. Hist. Surv., Bull. No. 70. 



Baker, F. C. 1939. Fieldbook of Illinois Land Snails. Illinois Natural History 

 Survey, Manual 2. Urbana, Illinois 



Baker, F. C. 1945. The Molluscan Family Planorh^dae. Univ. of 111. Press. 



164 



