PLATE XVIIa. 



(Figures 1-6, 8, 9, 11, 13, U, 21, 25, 26 by E. Emmons ; 6, 7, 10, 13, 15-20, 22-24 byG. B. Simpson.) 



Legend. A. Cardinal area (pedicle-valvo). x. Scar of attaehmont. 



D. Deltidium (pedicle-valve). z. Posterior ridj^e limitin},'- internal cavity. 



C. Deltidium (brachial valve). a. Anterior adductor scars, 



j. Cardinal process. a'. Posterior adductor scars. 



t. Teeth. r. Diductor scaiB. 



Genus STROPHALOSIA, King. 



(See Plates XVb and XVII.) 

 Page 314. 



Strophalosia Rockfordensis, sp. IIOV. 



Fig. 1. A view of an imperfect specimen which retains the cardinal ai-ea and deltidi\im of (^ach valve. X 2. 

 Fig. 2. Cardinal view of tlie same specimen ; showing the scar of attachment. X 2. 

 Upper Devonian. Rockford, Iowa. 



Strophalosia cymbula, sp. nov. 



Figs 3, 4. Opposite sides of the same specimen ; showing the cardinal areas, dellidia and scar of attachment. 



Keokuk group. Lebatwn, Ktrntucky. 

 Figs. 8, 9. Opposite sides of a larger individual, which is somewhat crushed at the apex of the brachial 

 valve. 



Keokuk group. South of Louisville, Kentucky. 



Strophalosia Keokuk, Beecher. 



Fig. 5. A small individual ; showing the great length of the spines. 



Fig. 6. An attached specimen ; showing deltidia, cardinal areas and adherent spines. X 2. 

 Fig. 7. The cardinal portion of the same specimen enlarged to show the prolongation of the deltidium into 

 a tube or sheath for the pedicle. X 4. 



Keokuk group. Oramfordsville, Indiana. 



Genus PRODUCTELLA, Hall. 



(See Plate XVII.) 

 Page 3-28. 



Peoductella, sp. (?) 



Fig. 10. Cardinal view of an undetermined species, which retains the cardinal areas and deltidia of both 

 valves and the marginal spines of the pedicle-valve. X 2. 

 Chemung group. Qreenwood, iV. T. 



Productella pyxidata. Hall. 



(See Plate XVII, Hg. 34.) 

 Fig. 14. The cardinal portion of the pedicle-valve ; showing the area and teeth. X 2. 

 Choteau limestone. Fike comity, Missouri. 



Genus PRODUCTUS, Sowerby. 



(See Plates XVIIL and XIX.) 

 Page 321. 



Productus (Marginifeea ? ?) DissiMiLis. Hall (= Productella Hallana, Walcott). 



Fig. 11. The interior of a pedicle- valve ; showing the sharp, papillose ridges or platforms diverging from 



the umbo. X 2. 

 Fig. 12. The interior of a brachial valve which shows cori-esponding pitted ridges diverging from the bases 



of the cardinal process. This specimen also shows the remarkably extended brachial areas. 



X 2. 



Upper Devonian. Liine Creek, lotoa. 



