PLATE XIII— Continucil. 



Stropheodonta (Leptosteophia) Becki. Hall. 



Fig. 23. The interior of a pedicle-valve. The delthyriuiii is exposed by the removal of the deltidium, and 

 the short dental lamellte have nnited, foi-niing a minute pedicle-pit. The muscular area is 

 bounded laterally by divergent papillose lidges which take their oi'igin at the extremities of 

 the dental lamellfe. 



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

 Lower Helderberg group. Schoharie, N. T. 



Stropheodonta magniventra. Hall 



Figs. 25, 26. Natural casts of the intei-ioi' of pedicle-valves ; showing the great development of the muscu- 

 lar a]-eas. 



Oriskany sandstone. Albany county, N. Y. 



Stropheodonta (Leptostrophia) magnifica, Hull. 



Fig. 27. The interioi' of a brachial valve, drawn from a gutta-percha impresision ; showing the character of 

 the cai'dinal process, which is foreshortened in the tigui'e, the obsolescent dental sockets, the 

 crural plates and the musculai' area. 



Oriskany sandstone. Albany coimty, N. T. 

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

 union of the dental lamellfe ; also the expanded, undefined muscular area. 

 Oriskany sandstone. Cumberland, Maryland. 



