Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
PLATE X. 
(Figures 1-H, 16,18-23 by K. P. Whitfield; 16, 17 by F. B. Meek.) 
Legend. D. Deltidium. 
A. Cardinal area. 
I. Umbo-lateral slopes, 
t. Teeth. 
d. Dental lamellae, 
b. Dental sockets. 
j. Cardinal process, 
c. Crura. 
s. Median septum, 
a. Adductor scars, 
r. Diductor scars. 
Genus ORTHOTHETES, Fischer dr Waldheim. 
Page 253. 
Orthothetes Chemungensis, Conrad, var. Pandora, Billings. 
1. A view from the brachial valve; showing the cardinal area and deltidium of the opposite valve. 
Corniferous limestone. Caledonia, N. Y. 
2. The interior of a brachial valve, drawn from a gutta-percha impression ; showing the muscular 
area, and, imperfectly, the cardinal process. 
Schoharie grit. Schoharie, N. Y. 
3. The interior of a larger brachial valve; showing with more accuracy the crural plates and the 
adductor scars. 
Plate IX, Fig. 30.—An enlargement of a part of the hinge area, the cardinal process, crural 
plates and muscular impressions of the preceding specimen. 
4. The interior of a pedicle-valve; showing the low deltidium, with unsupported teeth, the adductor 
and diductor scars. 
Corniferous limestone. Caledonia, N. Y. 
5. The interior of a pedicle-valve, drawn from a gutta-percha impression. 
Schoharie grit. Schoharie, IV. Y. 
6. An internal cast of the pedicle-valve; showing the flabellate diductors and the impression of a 
broad median ridge. 
Corniferous limestone. Western New York. 
Orthothetes Chemungensis, Conrad; var. alternata, Hall. 
7. The interior of the brachial valve ; showing the characteristic cardinal process. 
Hamilton group. Canandaigua Lake, N. Y. 
Orthothetes Chemungensis, Conrad, var. arctostriata, Hall. 
S. An internal cast of the pedicle-valve ; showing the impression left by the rather unusual develop¬ 
ment of the ridges surrounding the adductor scars and uniting irT the median line separating 
the diductors. This ridge is not a septum but merely the thickening of the edges of the mus¬ 
cular scars. X 2. 
Hamilton group. Western New York. 
Orthothetes Chemungensis, Conrad. 
9. A cardinal view of a specimen ; showing the irregular form of the shell, (the usual width of the 
area, and the character of the deltidium. 
Chemung group. South-westei'n New York. 
For further illustration, see Palaeontology of New York, Volume IV, plates ix and x. 
Genus DERBY A. Waagen. 
Page 261. 
Derbya crassa, Meek and Hayden. 
10. The interior of a brachial valve ; showing the cardinal process and muscular impressions. The 
former is represented as having the lobes upon its edge and too acutely angular. 
11. The interior of a pedicle-valve, with strong median septum dividing the muscular area, and 
highly developed teeth projecting into the cavity of the valve. 
Coal Measures. Near Winterset, Iowa. 
