MONOMBBELLA GbEENII, Hall. 



Page 328. 

 Fig. 9. An internal cast of the pedicle- valve; showing the extremely small 

 umbonal chambers and the sharply defined crescent, cardinal groove and 

 lateral scars . 



Fig. 10. An internal cast of a pedicle- valve; showing the very broad cardinal 

 margin and its lateral extent ; also the faint umbonal cavities and the con. 

 spicuous cardinal groove and crescent . 



Fig. 11. An internal cast of the brachial valve; showing in the matrix the 

 impression of the cardinal area. The platform scars are accompanied by 

 only a very faint thickening of the shell. 



Fig. 12. The interior of a brachial valve, from a gutta-percha cast of a natural 

 impression. The crescentic fulcrum is exceedingly stroAg and the plat- 

 form very obscure . 

 Niagara limestone . Grafton^ Wisconsin. 



Fig. 18 An internal cast of the brachial valve ; showing a portion of the broad 

 area of contact, the platform scars with the diverging anterior ridges . 

 Niagara limestone . Rising Sun, Ohio. 



Fig. 14. The interior of a brachial valve, with sharply defined terminal scars 

 and anterior ridges. From a gutta-percha cast. 

 Niagara limestone . Grafton, Wisconsin. 



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