20 Side view of ventral valve, showing convexity, x 2 

 2i, 22 Views of a ventral valve, x 2 



23 Interior of a dorsal valve, x 2 



24 A ventral valve, x 2 



25 Enlargement of sculpture, x 5 ; from fig. 26 



26 External cast of dorsal valve, showing the fine concentric sculpture, x 2 



27 A portion of the two valves, showing cardinal spines, x 4 

 28, 30 Interior of dorsal valves. (28, x 3 ; 30, x 2j 



29 Ventral valve, x 2 



Grande Grlve limestone ; division 2. Grande Greve 



335 



