PLATE LVIU— Continued. 



Subgenus PLETHORHYNCHA, s.-gen. nov. 



Page 191. 



Plethoriiyncha speciosa, Hall. 



Figs. 29-31. CariUnal, front and profile views of a larg-e entire individual ; showing- the robust form of the 

 shell, its subquadrate transvei'se section, serrate mai-gins and broad, somewhat concave latei-al 

 slopes. The abrupt marginal extensions of the cardinal slopes of the pedicle-valve, fitting 

 into corresponding excavations of the bi'achial valve, as shown in figures 29 and 30, are the 

 thiitkened teeth which are cemented to the walls of the shell throughout their entire extent and, 

 at their summits only, fitted into shallow sockets in the opposite valve. 



Fig. 32. The interioi- of a brachial valve, slightly broken about the margins ; showing a thickened, undi- 

 vided hinge-pliite, bilobed cardinal process, narrow dental sockets and the median septum. 



Fig. 33. A cardinal view of the same specimen ; showing the elevation of the cardinal process and crura 

 and the marginal excavations for the reception of the teeth. 



Fig. 34. Cardinal view of the umlional portion of an old shell in which the entire hinge-plate has become 

 greatly thickened and elevated, and the apical portion or cardinal process resorbed and exca- 

 vated. The projecting points above are the bases of the crura. 



Fig. 35. The interior of a small pedicle-valve ; showing the form of the teeth, and faint median muscular 

 ridge on the bottom of the valve. 



Fig. 36. The interior of a young brachial valve in which the hinge-plate is divided, its lateral portions i-est- 

 ing on the median septum, and the cardinal margins but slightly excavated for the reception of 

 the teeth. 



Fig. 37. Theumbonal portion of the same specimen, enlarged ; showing the small cardinal process and the 

 median division of the hinge-plate resting on the septum and forming an incipient spondylium. 



X 2. 



Oiiskany sandstone. Cumberland, Maryland. 



Genus UNCINULUS, Bayle. 



Page 195. 



Uncinulus (Uncinulina) Stkicklandi, Sowerby. 



Fig. 38. Cardinal view of an internal east of both vahes, the brachial valve being represented above ; 

 showing the cavities representing the median septum, the cardinal process and hinge-plate, 

 and the ridge tilling the median division of the latter. 

 • Niagara dolomites. Near Milwaukee, Wisconsin. 



Figs. 39, 40. Dorsal and cardinal views of the exterior of a normal adult; showing the low median fold and 

 the smooth cardinal slopes. 



Niagara group. Waldron, Indiana. 



