PLATE XVIIa. 



(Figures 1-fi, 8, 9, 11, 12, 14, 21, 25, 26 by E. Emmons ; 6, 7, 10, 13, 15-20, 22-24 by G. B. Simpson.) 



Leg'end. A. Cardinal area (pedicle-valve). x. Scar of attachment. 



D. Deltidium (pedicle-valve). z. Posterior ridge limiting: internal cavity. 



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



j. Cardinal process. a'. Posterior adductor scai-s. 



t. Teeth. r. Diductor scars. 



Genus STROPHALOSIA, King. 



(See Plates XVb and XVII.) 

 Page 314. 



Strophalosia Rookfordensis, sp. uov. 



Fig. 1. A view of an imperfect specimen which I'etains the cardinal area and deltidium of each valve. X 2. 

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

 Upper Devonian. Rookford, Iowa. 



Strophalosia ctmbula, sp. nov. 



Figs. 3, 4. Opposite sides of the same specimen ; showing the cai'dinal areas, deltidia and scar of attachment. 



Keokuk group. Lebanon, Kmitucky. 

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

 valve. 



Keokuk group. South of Lcmismlle, 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. Orawfordsville, Indiana. 



Genus PEODUCTELLA, Hall. 



(See Plate XVII.) 

 Page 328. 



Peoductella, sp. (?) 



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

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

 Chemung group. Gheenwood, N. Y. 



Produotella ptxidata. Hall. 



(See Plate XVII, fig. 34.) 

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

 Choteau limestone. Pike county, Missouri. 



Genus PRODUCTUS, Sowerbt. 



(See Plates XVI 11 and XIX.) 

 Page 321. 



Productus (Mabginifera ? ?) 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 corresponding pitted ridges diverging from the bases 



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



X 2. 



Upper Devonian. Lime Creek, Iowa. 



