PLATE XIII—Continual. 
Stropheodonta (Leptostrophia) Becki. Hull. 
Fig. 23. The interior of a pedicle-valve. The delthyriuin is exposed by the removal of the deltidium, and 
the short dental lamella; have united, forming a minute pedicle-pit. The muscular area is 
bounded laterally by divergent papillose ridges which take their origin at the extremities of 
the dental lamellae.. 
Fig. 24. The exterior of a brachial valve ; showing the concentric undulations. 
Lower Helderberg group. Schoharie, N. Y. 
Stropheodonta magniventra. Hall 
Figs. 25, 26. Natural casts of the interior of pedicle-valves ; showing the great development of the muscu¬ 
lar areas. 
Oriskany sandstone. Albany county, N. Y. 
Stropheodonta (Leptostrophia) magnifica, Hall. 
Fig. 27. The interior of a brachial valve, drawn from a gutta-percha impression ; showing the character of 
the cardinal process, which is foreshortened in the figure, the obsolescent dental sockets, the 
crural plates and the muscular area. 
Oriskany sandstone. Albany county, N. Y. 
Fig. 28. The interior of a pedicle-valve ; showing the formation of a pedicle-pit in the delthyrium, by the 
union of the dental lamellae ; also the expanded, undefined muscular area. 
Oriskany sandstone. Cumberland, Maryland. 
