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PLATE XV. 
(Figures 1-36 by R. P. Whitfield.) 
Legend, v. Pedicle-valve. 
d. Brachial valve. 
A. Cardinal area. 
D. Deltidium. 
A. Delthyrium. 
t. Teeth. 
b. Dental sockets. 
j. Cardinal process, 
c. Crura. 
s. Median septum, 
r. Diductor scars, 
a. Anterior adductors, 
a'. Posterior adductors. 
Genus STROPHEODONTA, Hall. 
Page 284. 
Stropheodonta corrugata, Conrad. 
1. The exterior of a pedicle-valve; showing the corrugations along the cardinal margin. 
Clinton group. Western New York. 
Stropheodonta (Leptostrophia) perplana, Conrad. 
2. View of the brachial valve ; showing the cardinal area of the opposite valve. 
Corniferous limestone. Western New York. 
3. The pedicle-valve of a smaller specimen. 
Hamilton group. Western New York. 
4. The exterior of a pedicle-valve; showing the alternation in size of the striae. 
5. An enlargement of the striae from the same specimen. 
Hamilton group. New Buffalo, Iowa. 
6. A similar enlargement where the striae are of equal size. 
7. The interior of a pedicle-valve ; showing the uninterrupted cardinal area and the thickened pus- 
, tulose lateral margins of the muscular area. 
Hamilton group. Western New York. 
8. The interior of a pedicle-valve retaining similar characters. 
Hamilton group. New Buffalo, Iowa. 
9. An enlargement of the interior umbonal portion of the brachial valve ; showing the cardinal pro¬ 
cess and lateral muscular ridges. X 2. 
Hamilton group. Canandaigua Lake, N. Y. 
10. The cardinal process, enlarged to show the grooving of the posterior surface of the lobes for the 
attachment of the diductor muscles. X 3. 
11. The cardinal areas of both valves; showing the uninterrupted striated surface. X 1$. 
12. A longitudinal axial section of the two valves ; showing the normal curvature of the shell and the 
position of the cardinal process. 
13. An enlargement of the surface as left by the removal of the shell. 
Hamilton group. Western New York. 
Stropheodonta perplana, Conrad, var. nervosa, Hall. 
14. A portion of a pedicle-valve; showing the irregular character of the striae. 
15. An enlargement of a portion of the same. 
17. A specimen showing the wrinkled striae and extended cardinal angles. 
Chemung group. Steuben county, N. Y. 
Stropheodonta (Leptostrophia) Junia, Hall. 
16. A portion of the pedicle-valve ; showing the crenulated area and partially covered delthyrium. 
Hamilton group. Canandaigua Lake, N. Y. 
Stropheodonta (Douvillina) Cayuta, Hall. 
18. An internal cast of the pedicle-valve; showing the short, transverse, sharply defined muscular 
scar. 
19. An enlargement of the muscular area of the same specimen. X 2. 
Chemung group. Steuben county, N. Y. 
