U.S. GEOLOGICAL SURVEY 



MONOGRAPH !X PLATE XI. 



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31 



29 y 





V^ 



36. 





R P Wni ' f i el d , d ' 



T Sir.ciair * £o7'. Phiia 



LAMELLIBRANCHIATA . 



(CR ETACEOUS - LO\\ER MARL 3 E D S .) 



