PLATE XVb—C ontinued. 
Chonetes Amazonica, Derby. 
Fig. 13. An enlargement of an internal cast of the pedicle-valve, which retains the filling of the spine-tubes 
crossing the cavity left by the removal of the cardinal portion of the valve. X 3. 
Coal Measures. Rio Tapajos, Brazil. 
Genus CHONOSTROPHIA, gen. nov. 
(See Plate XVI.) 
Page 310. 
CHONOSTROPHIA HELDERBERGIA, sp. 110V. 
Fig. 14. A specimen in which the valves are opened, exposing their internal surfaces. The shell may have 
been somewhat flattened in fossilization, but still shows the reversal of the relative convexity of 
the valves, the cardinal area, teeth and faint median septum of the pedicle-valve and the finely 
lineate surface. The cardinal process is not retained with sufficient distinctness to permit its 
accurate delineation. 
Lower Helderberg group. Near Clarksville, N. Y. 
CHONOSTROPHIA REVERSA, Whitfield. 
Fig. 15. The exterior of a pedicle-valve ; showing its gentle concavity and fasciculate ornamentation. X 2. 
Corniferous limestone. Delaware, Ohio. 
Fig. 16. The exterior of a pedicle-valve which retains the cardinal spines. X 2. 
Fig. 17. The interior of a brachial valve; showing the contour of the shell and retaining the cardinal pro¬ 
cess. X 2. 
Upper Helderberg group. Cayuga, Ontario. 
Fig. 18. An enlargement of the cardinal process and crural plates. The former is bilobed but short, and 
terminates abruptly at the base. The crural plates are also quite short and have a slightly sin¬ 
uous curvature. X 6. 
Fig. 19. An enlargement of the surface striae; showing their fasciculate grouping. X 6. 
Corniferous limestone. Delaware, Ohio. 
Genus CHONOPECTUS, gen. nov. 
(See Plate XYI.) 
Page 312. 
Chonopectus Fischeri, Norwood and Pratten. 
Fig. 20. The exterior of a pedicle-valve which retains the reticulate surface ornamentation and a large scar 
of attachment. X 2. 
In strata referred to the age of the Waverly group. Warren, Pennsylvania. 
Fig. 21. Ajpedicle-valve having the normal proportions of the species, and showing a few spine-bases on 
the cardinal margin. The reticulate surface markings, as on this specimen, do not usually ex¬ 
tend over the pallial region, which is covered by exceedingly fine, often irregular radiating 
striae, 
Fig. 22. Posterior view of the umbonal region in the same specimen, enlarged to show character of the 
cicatrix. X 2. 
Fig. 23. A small pedicle-valve, retaining the cardinal spines and showing, over the body of the shell, some 
divergent impressions which may be of vascular origin. 
Yellow sandstones. Burlington, Iowa. 
Genus STROPHALOSIA, King. 
(See Plates XVI, XVII, XVIIa.) 
Page 314. 
Strophalosia truncata, Hall. 
Fig. _24. An internal cast of a pedicle-valve; showing the muscular impressions; enlarged. 
Fig.] 25. The interiorof a pedicle-valve ; enlarged. 
Fig. 26. The exterior of a pedicle-valve ; showing the spiniferous surface ; enlarged. 
Marcellus shales. New York. 
