PLATE 5Vb— Continued. 



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. aov. 



Fig. 14. A specimen in which the valves are opened, exposing tlieii' 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 iinely 

 lineate sui-face. The cardinal process is not retained with sufficient distinctness to permit its 

 accurate delineation. 



Lower Helderberg group. Near Clarksville, N. T. 



Choncstrophia reversa, Whitfield. 



Fig. 15. The exterior of a pedicle-valve ; showing i^s gentle concavity and fasciculate ornamentati( n. X 2. 



Corniferous limestone. Delaware, Ohio. 

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



Fig. 17. The interior of a brachial valve ; showing the contoui- of the shell and retaining the cardinal pi'o- 

 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 strise ; showing their fasciculate grouping. X 6. 

 Corniferous limestone. Delaware, Ohio. 



Genus CHONOPECTUS, gen. nov. 



(See Plate XVI.) 



Page 313. 



Chonopectus Fisoheri, 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 sti-ata referred to the age of the Waverly group. Warre?i, 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 

 stidse. 



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 trungata, 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. 



