EXPLANATION OF PLATE XLH. 



PtEria pKTkosa { Cunra.l ) P- 429 



1. A cuniplclc iiitcnial cast of Uic riylit valve, 



Cliffii'oud day: near Malaz^'aii. (iSo). 



2. All incom|)k'te internal cast 'if a left val\-e. 



ilVi'iioiiali sand: near Marlhurn, (130). 



PtERIA lakipES (^liirton), P- 431 



3. View of a left valve. (After Whiliield.) 



PtERIA naviclt.a Whitfield, p. 432 



4. View of the type specimen. ( .\ftei" A\'liithelel. ) 



W'aodbiiry cliiy: 1 1 addnnficld . (JS^). 



MeeEAGRinKlla aeropTa ( Conrad ) V- 433 



5_6. Vie\vs of two intern.al ca^ts. a left wahc and a right valve. 



Na-i'csiiiL' marl: near Hohndcl, {rsS'). 

 7-S. Internal and external \ic\vs of a nearly complete right valve, 

 fx2). (After Whitheld. ) 

 9. The hinge of a left valve, (.x_'l. (After Whitheld.) 

 Na-eesink marl: Freeludd. 



OstrEa p.\nda Morton p. 437 



10. View of .a nearly jicrfect hjwcr \alve. 



iMaishallhizeii elay-niarl: near S'Teedesboro, (iSo). 



OsiREA ckE'i'.vcEA ^[ortrin, p. 434 



11. »A nearly complete internal cast of the lower vahe. 



Cliffxeoed elay: Cliffzeuod Paint iJOj). 



OSXRE.V CkENl'I.l-MARi'.lX.MA ( ",,lhl) p. 44I 



12-13. External .and intern.al \ie\vs "f .a cuniiilete single \'alve. illus- 

 trated hy Whitlield. 



A'az'esinL- marl: Marlboro. 



OSTRE.V sji. 



14. View ot an internal ca^t of :■, lower val\e. 



f ineenli'zeii sand: near IJeal, (/J'J'). 



OsTREA SUIlSPATLlLA'tA I'nrlies p. 440 



15. View of an internal cast of a lower \ahe. 



Il'enonuh sand; Crawfords Corner (126'). 



OsTREA PLLI-MOSA jNIorton p. 439 



16. An upper vahe [ireserxdng the shell. 



17. A lower valve siiiiposed to hclong to this species. 



ilarslialltoien elay-marl: near Sieedesboro. (i~y). 



18. Internal cast of a lower vah'e. 



IVeiionali sand: Crazefords Corner (126'). 



966 



