PLATE XVb— Continued. 



Chonetes Amazonica, Derby. 



Fig. IS. An enlargement of an internal cast of the jiedicle-valve, which retahus the tilling of the apine-tubes 

 crossing the cavity left by tho 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 Heldekbekgia, sp. UOV. 



Fig. 14. A specimen in whi.h the valves are openeil, exposing their internal suiface.s. The shell may have 

 been somewhat flattened in foasilization, 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 sufKcient distinctness to permit its 

 accurate delineation. 



Lower Helderberg group. Near Clarksville, N. T. 



Chonostrophia reversa, Whitfield. 



Fig. 15. The exterior of a pedicle-valve ; showing its gentle concavity and fasricidate ornamentalic n. X 2. 



Corniferous limestone. Delaware, Ohio. 

 Fig. 16. The exterior of a pedicle-valve which retains the cardinal spines. X 2. 



Fig. 17. The interioi' of a brachial valve ; showng 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 shoit, 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 striaj ; showing their fasciculate grouping. X 6. 

 Corniferous limestone. Delaware, Ohio. 



Genus CHONOPECTUS, gen. nov. 



(See Plate XVI.) 

 Page 312. 



Chonopectus Fisgheei, Noi-vvood 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 sti-ata referred to the age of the Waverly group. Warreii, Pen-n-sylvania. 



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 i-adiating 

 striae. 



Fig. 22. Posterior view of the umbonal region in the same specimen, enlarged to show character of the 

 cicati-ix. 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 oi'igin. 

 Yellow sandstones. Burlington, lima. 



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. J 25. The interior of a pedicle-valve ; enlarged. 



Fig. 26. The exterior of a pedicle-valve ; showing the spiniferous surface ; enlarged. 

 Marcellus shales. New York. 



