I'LATE XLII— Continued. 



Genus CHARIONELLA, Billings. 



Page 78. 



Charionella scitula, Billings. 



Fig. 17. Dorsal view of a .specimen fiiim which a portion of the shell has been removed exposing the mue- 

 eular impressions of the brachial valve and the median thickening of the hinge. 



Fig. 18. An intei-nal cast of the pedicle-valve ; showing the impression of the muscular area and traces of 

 the radiating lines on the inner laminffi of the shell. 



Fig. 19. The cardinal portion of the biachial valve. The hinge-plate in this genus takes the form of a 

 concave thickening adherent to the bottom of the valve. That portion of it which foi-ms the 

 socket-walls lies close against the margins of the valves making .very naiTow dental sockets. 

 The crura arise from the inner extremities of these walls. 

 Corniferous limestone. Cayuga, Ontario. 



Chauionella Hyale, Billings. 



Figs. 20, 21. Two views of an intei-nal cast, having a hinge-structure similar to that in the preceding species. 

 Guelph limestone. Ouelph, Ontario. 



Genus PENTAGONIA, Cozzens. 



Page 80. 



Pentagonia unisulcata, Conrad. 



Fig. 22. The exteiior of a pedicle-valve ; showing the broad, angular median sinus. 



Fig. 2'i. A cardinal view of the same specimen ; showing the median sinus on each valve and the single pair 



of cardinal folds on the brachial valve. 

 Fig. 24. Anterior marginal view of the same specimen j showing the elevation of the median fold of the 

 brachial valve. 



Corniferous limestone. Western Ne^e York. 

 Figs. 25, 26. Profile and cardinal views of a specimen which has no sinus on the fold of the bi achial valve. 



Hamilton group. Ceiiterfield, N. T. 

 Fig. 27. The hinge-plate as viewed from the front ; showing the erect position of the crura. 

 Fig. 28. The same specimen viewed from above ; showing the deep central excavation of the hinge-])late, 



the form of the socket-walls and the position of the crura. X 3. 

 Fig. 29. A preparation, showing the form of one of the spiral cones and of a portion of the loop. It is 

 probable that the latter feature is incomplete, (c.) 

 Hamilton group. Western New York. 

 Fig. 30. The interior of a brachial valve ; showing articulating processes, muscular impression and short, 

 low median septum. 



Corniferous limestone. Falls of the Ohio. 

 Fig. 31. Cardinal view of a shelKwith two pairs of folds on the posterioi- margin of the brachial valve. 

 This is the form which has been termed var. MpHcata. 

 Hamilton group. Darien, N. Y. 

 Fig. 32. The interior of an imperfect pedicle-valve ; showing the articulating apparatus and muscular im- 

 pressions. 



Corniferous limestone. Falls of the Ohio. 



