PLATE 43. 
Legend: hp. Hinge-plate. a, Adductor scars, 
b. Dental sockets. . Diductor’scars. 
d, Spondylium. v. Vascular sinuses, 
j. Cardinal process. . Callosities in the umbonal region. 
c. Crural bases. 
La] 
‘a 
CAMAROTC@OHIA, Hatt. 
Page 826. 
CaMAROT@CHIA CONGREGATA, Hall. 
Figs. 1, 2, 3. Dorsal, ventral and cardinal views of a typical specimen. 
Figs. 4, 5. Enlargements of the hinge-plate; showing its median division by an 
incipient spondylium and the crenulation of the dental sockets. 
Fig. 9. Cardinal view of an internal cast; showing the cavities of the denta. 
plates and median septum. 
Hamilton group. Sandy shales of Central New York. 
CamaroTacuia conTracra, Hall. 
Fig. 6. An internal cast of the pedicle-valve ; showing the muscular scars. 3 
Hamilton group. Near Cardiff, N. Y. 
CAMAROT@CHIA OKBICULARIS, Hall. 
Fig. 7. An internal cast of the pedicle-valve; showing the adductor and 
diductor scars. * 3. 
Fig. 8. Cardinal view of an internal cast; showing the filling of the rostra 
cavity and the extent of the thickened median septum. 
Chemung group. Meadville, Pennsylvania, 
PiETHORHYNCHA, Hatt. 
Page 827. 
PLETHORHYNCHA sPEcrIosa, Hall. 
Fig. 10. Cardinal view of the brachial valve of an old shell in which the entire 
hinge-plate has been greatly thickened and the apical portion, or 
cardinal process, resorbed and excavated. 
Figs. 11, 14. Two views of the brachial valve; showing the thickened hinge- 
plate, bilobed cardinal process and strong median septum. 
Fig. 12. The hinge-plate of a young shell; showing its median division and 
small cardinal process. X 2. 
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