IMjATK Mil— Contlliucil. 



Stropheodonta (LEPTOSTROrHiA) Becki, Hall. 



Fig. 23. The interior of a pedicle-valve. The delthyriuiii is exposed l>y the reimival of the deltidimn, and 

 the short dental lamelUe have united, forming a minute pedicle-pit. The nuKscular area is 

 bounded laterally by divergent papillose ridges which take their origin at the extremities of 

 the dental lamella'. 



Fig. 24. The exterior of a bi-achial valve; showing the concentric undulations. 

 Lower Helderberg group. Schtharie, N. Y. 



Stropheodonta magniventra. Hall 



figs. 25. 26. Natural casts of the interioi' of pedicle-valves ; showing the great development of the muscu- 

 lar areas 



Oriskany sandstone. Albany county. N. Y. 



Stropheodonta (Leptostkophia) magniitca, Hall. 



Fig. 27. The interior of a brachial valve, drawn fi-om a gutta-percha impre.';sion ; .showing the character of 

 the cardinal process, which is foi'eshortened in the figure, the obsolescent dental sockets, the 

 crural plates and the muscular area. 



Oi-iskany sandstone. Albany county. N. Y. 

 Fig. 28. The interior of a pedicle-valve ; showing the formation of a pedicle-pit in the delthyriuin, by the 

 union of the dental lamellie ; also the expanded, undetined muscular area. 

 Oriskany sandstone. Cumberland, Maryland. 



