PLATE XVb— Continued. 



Chonetes Amazonica, Derby. 



Fig. 13. An enlargement of an internal cast of the jieilicle- 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 CHONOSTKOPHIA, oex. nov. 



(See Plate XVI.) 

 Page 310. 



Chonostrophia Heldekbekoia, sp. IIOV. 



Fig. 14. A specimen in whiih Ihe valves are openeil, exposing llieir internal suitace.-i. The shell may have 

 been somewhat flattened in fossilization, but still shows the reversal of the relative convexity of 

 the valves, the oai-dinal ai-ea, teeth and faint median septum of the pedicle-valve and the linely 

 lineate surface. The cardinal process is not retained with sufficient distinctness to permit its 

 accurate delineation. 



Lower Helderberg group. Near Clarksville, N. F. 



Chonostrophia reveksa, Whitfield. 



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



Cornifei-ous limestone. Delaware, Ohio. 

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



Fig. 17. The interioi' of a brachial valve ; showing the contour of the shell ami retaining the caniinal pro- 

 cess. X 2. 



Upper Helderberg group. Cayuga, Ontario. 

 Fig. 18. An enlargement of the cardinal process and crural plates. The foi-mer is bilobed but shoi t, and 

 terminates abruptly at the base. The crural jjlates 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 tJ. 

 Cornifeions limestone. Delaware, Ohio. 



Genus CHONOPECTUS, gen. nov. 



(See Plate XVI.) 

 Page 31-2. 



Chonopeotus Fisgheri, Noi-vvoud and Pnitteii. 



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, Peniisylvania. 



Pig. 21. A_!pedicle-valve having the normal pi-oportions of the species, and showing a few spine-bases on 

 the cardinal margin The retii.'ulate 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 

 cicatnx. X 2. 



Fig. 23. A small pedicle-valve, i-etaining 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, XVI1.\.) 

 Page 314. 

 Strophalosia TRUNCATA, Htlll. 

 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. 



