I'LATK Xlll-Colitinucl. 



Stropheooonta (LErTOSTROi'HiA) Becki, Hall. 



Fig-. 23. The interior of a pedicle-valve. The delthyriuni is exposed l,y the removtil of the deltididiii, and 

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

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

 the dental lamella". 



Fig. 2-1. The exterior of a brachial valve; showing the concentric undulations. 

 Lowei' Helderbei-g group. Schoharie, JV. Y. 



Stkopheodonta magniventea. Hall 



Figs. 25, 26. Natural casts of the interioi' of pedicle-valves ; showing the gi-eat development of the muscu- 

 lar aieas 



Oriskany sandstone. Albany cmonty, N. Y. 



Stropheooonta (Leptostkophia) magnifica, Hall. 



Fig. 27. The intei-iorof a brachial valve, di-awn from a gutta-percha inipres-sinn ; showing the character of 

 the cai-dinal 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 foimation of a pedicle-pit in the delthyrium, by the 

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

 Oriskany sandstone. Cumberland, Maryland. 



