PLATE SVI— Continued. 



Chonetes coeonata, Conrad. 



Fiy. 10. A view of the lii-achial valve j showing' the cardinal ai-ea ami deltiiiiinn. 

 Fig-. 11. A pedicle-valve with unusually strong' concenti-ic growth-lines. 



Hamilton group. Daneii, N. F. 

 Fig. 24. The interior of a brachial valve ; showing the cardinal process, muscular scars and brachial 

 i-idges. 



Hamilton group. York, N. Y. 

 Fig. 26. The interior of another brachial valve ; showing moi'e distinctly the quadripartite character of the 



cardinal process. 

 Fig. 33! The interior of a pedicle-valve ; showing the cardinal area, teeth and muscular scars. 



Hamilton group. Western New York. 



Genus STROPHALOSIA, King. 



(See Plates XVb, XVII, XVIIa.) 

 Page 3U. 



Strophalosia muricata, Hall. 



Fig. 12. The exterior of the pedicle-valve, from a gutta-percha impression of a natural mould ; showing the 



short spines on the surface. 

 Fig. 16. Two views of a pedicle- valve ; showing the cicatrix of attachment. 

 Fig. 30. The interior of a bi-achial valve, from a gutta-percha impi'ession ; showing the cardinal process, 



bi-achial ridges and median septum. 

 Fig. 38. An internal cast of the pedicle-valve ; showing the muscular impressions. 



Fig. 42. An enlargement of the muscular scars restored from several internal casts of the pedicle-valve. 

 Chemung group. Meadville, Pennsylvania. 



Genus CHONOSTROPHIA, gen. nov. 



^(See Plate XVb.) 

 Page 310. 



Chonostrophia complanata, Hall. 



Fig. 13. The intei'ior of the pedicle-valve tVom a gutta-percha impression ; showing the reversed convexity 



of the shell, the flabellate muscular area, conspicuous median septum, and the cardinal spines. 

 Fig. 29. Another interior of a similar valve in which the cardinal spines are apparently absent. 

 Oriskany sandstone. Albany county, N. Y. 



Genus CHONETES, Fischer de Waldheim. 



Page 303. 



Chonetes hemisph^erica, Hall. 



Fig. 14. A view of the pedicle-valve ; showing its great convexity. 

 Schoharie grit. Albany county, N. Y. 



Chonetes arcuata, Hall. 



Fig. 15. Profile of a pedicle-valve, from which the radiating striie have been accidentally omitted in litho- 



gi'aphing. 

 Figs. 35, 36. Two views of an internal cast of the pedicle-valve ; showing the muscular impressions and the 



crenulation of the cardinal area, caused tjy the casts of the spine-tubes. 

 Corniferous limestone. Near Williamsville, N. Y. 



Genus CHONOPECTUS, gen. nov. 



(See Plate XVb.) 

 Page 312. 



Chonopectus Fischeri, Norwood and Pratten. 



Fig. 17. The extei'ior of a pedicle-valve ; showing the concentrii^ally reticulate sui'lace. 

 Fig. 31. An enlargement of the surface ; showing the double series of conceutiic wiinkles crossing the fine 

 radiating strije. 



Yellow sandstones. Burlington, Iowa. 



