PLATE LTin— CoDtinaed. 



Subgenus PLETIIORHYNCHA, s.-qen. nov. 



Page 191. 

 PlETHORHYNCHA 8PECIOSA, Hilll. 



Figv. 29-31. Cardinal, front and profile views of a large entire individual ; showing the robust form of the 

 shell, its subquadrate transvei'se section, serrate margins and broad, somewhat concave lateral 

 8lo|>es. The abrupt marginal extensions of the cardinal slopes of the pedicle- valve, fitting 

 into corresponding excavations of the brachial valve, as shown in figures 29 and 30, ai-e the 

 thirkened 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. 



Rg. 32. The interior of a brachial valve, slightly bi-oken about the mai'gins ; showing a thickened, undi- 

 vided hinge-plate, bilobed cardinal pi-ocess, narrow dental sockets and the median septum. 



Kg. 33. A canlinal 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. Cai-dinal view of the umbonal 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 ai-e the bases of the cmra. 



Rg. 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. 



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

 ing on the median septum, and the cai-dinal margins but slightly excavated for the reception of 

 the teeth. 



Kg. 37. The umbonal 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. 



Oriskany sandstone. Cumberland, Maryland. 



Genus UNCINULUS, Bayle. 



Page 196. 



Uncinulus (Unoinulina) Stuicklandi, Sovverby. 



Fig. 38. Cardinal view of an internal cast of both valves, the brachial valve I>eing represented above ; 

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

 and the ridge filling the median division of the latter. 

 • Niagara dolomites. Near Milvxiukee, Wisconsin. 



Figs. 89, 40. Dorsal and cardinal views of the exterior of a normal adult ; showing the low median fold and 

 the smooth cardinal slopes. 



Niagara g^oup. Waldron, Indiana. 



