PLATE 54. 
Legend: ch. Chilidium. b. Dental sockets. 
j. Cardinal process. r. Subrostral plate. 
TROPIDOLEPTUS, Hatz. 
Page 870. 
TROPIDOLEPTUS OccIDENS, Hall. 
Figs. 1, 2. Dorsal and ventral views of the original specimens of this species. 
Hamilton group. Iowa City, Iowa. 
TROPIDOLEPTUS CARINATUS, Conrad. 
Fig. 8. The pedicle-valve of a very young shell with acuminate cardinal 
extremities and coarse, simple and sharp plication. 3. 
Hamilton group. Canandaigua Lake, N. Y. 
Fig. 4. An enlargement of an interior layer of the shell, showing the puncte. 
Figs. 5, 6, 7. Ventral, profile and dorsal views of an average example; showing 
the exterior characters. 
Fig. 8. Cardinal view of the umbonal portion of the valves; showing the open 
delthyrium and the great development of the chilidium. * 3. 
Fig. 9. The interior of a brachial valve; showing, the cardinal process, 
crenulated dental sockets and median septum. 
Fig. 10. An internal cast of a brachial valve; showing the impression of the 
cardinal process and crenulated dental sockets. 
Fig. 11. The interior of a pedicle-valve; showing the cardinal area, open 
delthyrium and the prominent crenulated teeth, 
Hamilton group. From various localities in the argillaceous 
and arenaceous shales of Central and Western New York. 
EICHWALDIA, PBittiryes. 
Page 903. 
EIcHWALDIA RETICULATA, Hall. 
Fig. 12. Dorsal view of a very young example. X10. (After BEECHER and 
CLARKE.) 
Fig. 18. Dorsal view of an average mature specimen. X 2. 
Fig. 14. The interior of the umbonal portion of the pedicle-valve; showing the 
subrostral plate. * 2. 
Fig. 15, The interior of a brachial valve; showing the cardinal process and the 
marginal grooves for the reception of the ridges of the opposite 
valve. X 2. 
Fig. 16. The interior of the pedicle-valve; showing the open delthyrinm aud 
the linear ridges on the lateral margins. X 2. 
Niagara group. Waldron, Indiana. 
266 
