ErcHwaLpia concrnna, Hall.- 
Fig. 17. Dorsal view of the original specimen. 
Niagara group. Perry county, Tennessee. 
ErcHWALpDIA @1BB0sA, Hall. 
Fig. 18. Dorsal view of the original specimen. 
Niagara group. Perry county, Tennesee. 
EIcHWALDIA SUBTRIGONALIS, Billings. 
Figs. 19, 20, 21. Dorsal, cardinal, and front views ; showing the smooth surface 
of the valves and the ‘‘ bare-spot” or pedicle-aperture. 
Fig. 22. Dorsal view of a specimen in which the brachial valve is so broken as 
to expose its median septum. 
Black River limestone. Pauquette’s Rapids, Canada. 
AULACORHYNCHUS, Dirrmar. 
Page 904. 
AULACORHYNCHUS MILLEPUNCTATUS, Meek and Worthen. 
Fig. 23. The exterior of a pedicle-valve from which a portion of the shell has 
been exfoliated ; showing the inner surface of the triangular 
platform. 
Fig. 24. Avery large brachial valve; showing the outline and surfaee characters. 
Coal measures. Crooked Creek, Illinois. 
267 
