24 A ventral valve 



25 Dorsal exterior view 



26 Interior of the cardinal part of the dorsal valve with hinge process ; 



showintr also a mold of the external surface 



27 Interior of the dorsal valve, showing the cardinal process and very long 



oblique sockets and socket walls 

 Grande Grcvc limestone ; divisions i, 2, 3. Figures 16-18, 20, 24, 25, 

 •27, division i. Grande Greve ; 19, 21, 22, 23, 26. Perce Rock 



343 



