PLATE XLII—Continued. 
Genus CHARIONELLA, Billings. 
Page 78. 
Charionella scitula, Billings. 
Dorsal view of a specimen from which a portion of the shell has been removed exposing the mus¬ 
cular impressions of the bi-achial valve and the median thickening of the hinge. 
An internal cast of the pedicle-valve; showing the impression of the muscular area and traces of 
the radiating lines on the inner laminfe of the shell. 
The cardinal portion of the brachial 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 forms the 
socket-walls lies close against the mai'gins of the valves making „very narrow dental sockets. 
The crura arise from the inner extremities of these walls. 
Corniferous limestone. Cayuga, Ontario. 
Charionella Hyale, Billings. 
Figs. 20, 21. Two views of an internal cast, having a hinge-structure similar to that in the preceding species. 
Guelph limestone. Guelph, Ontario. 
Genus PENTAGONIA, Cozzens. 
Page 80. 
Pentagonia unisulcata, Conrad. 
Fig. 22. The exterior of a pedicle-valve ; showing the broad, angular median sinus. 
Fig. 23. 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 ; showing the elevation of the median fold of the 
brachial valve. 
Coi-niferous limestone. Western New York. 
Figs. 25, 26. Profile and cardinal views of a specimen which has no sinus on the fold of the brachial valve. 
Hamilton group. Ce7iterfield, N. Y. 
Fig. 27. The hinge-plate as viewed from the fi-ont; showing the erect position of the crura. 
Fig. 28. The same specimen viewed from above ; showing the deep central excavation of the hinge-plate, 
the form of the socket-walls and the position of the crura. X 3. 
Fig. 29. A x^reparation, showing the foi-m of one of the spiral cones and of a portion of the loop. It is 
X^robable 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 shelFwith two pairs of folds on the posterior margin of the brachial valve. 
This is the form which has been tei’med var. hiplicata, 
Hamilton group. Darien, N. Y. 
Fig. 32. The interior of an imperfect x^edicle-valve ; showing the articulating apxiaratus and muscular im¬ 
pressions. 
Corniferous limestone. Falls of the Ohio. 
Fig. 17. 
Fig. 18. 
Fig. 19. 
