PLATE XVIII. 



(Figures 1-5, 11-17, 19 by R. r. Whitfield ; 6-13, 18 by F. B. Meek.) 



Legend, j. Cardinal process. a. Anterior adductors. 



s. Septum. a'. Posterior adductors. 



V. Brachial ridges. r. Diductors. 



Genus PRODUCTUS, Sowbrby. 



(See ^Plates XVIIa, and XIX.) 

 Page 321. 



Peoductus Newbereyi, Hall. 



Fig. 1. The exterior of a pedicle- valve ; showing the numerous spine-bases and retaining the spines at the 

 cardinal extremities. 



Waverly sandstone. Medina, Ohio. 

 Fig. 2. An internal cast of the united valves ; .showing the muscular impressions of the brachial valve and 



the brachial i-idges. 

 Fig. 3. An internal cast of a pedicle-valve ; showing the adductor and diductor impressions. 

 Waverly sandstone. Newark, Ohio. 



Peoductus, sp. ? coiiipave Pkattenanus, Norwood. 



Fig. 4. An undetermined pedicle-valve belonging to the group of the Striati. 

 Waverly sandstone. Newark, Ohio. 



Peoductus, ? sp. ? 



Fig. 5. Pi'o61e of a pedicle-valve, with spiniferous costas. 



Chemung group. Cattaraug^ts county, N. T. 



Peoductus Flemingi, Sowerby, var. Buelingtonensls, Hall. 



Figs. 6, 7, 8. Three views of a pedicle-valve. 



Burlington limestone. Burlington, Iowa. 



Peoductus mesialis, Hall. 



Figs. 9, 10. Two views of a xaedicle-vah'e. 



Keokuk grouii. Nanvoo, Illinois. 



Peoductus semieeticulatus, Martiu. 



Fig. 11. A cast of the exteiioi' of a large brachial valve ; showing the sui'face characters. 

 Fig. 12. A cardinal view of the pedicle- valve. 



Fig. 13. A view of a specimen having the valves united and nstaining some of the cardinal spines on the 

 pedicle-valve. 



Keokuk group. Warsaw, Illinois. 



Peoductus alteenatus, Norwood and Pratten. 



Fig. 14. A pedicle-valve with the i:ieculiar suiface markings, which are due to the exfoliation of the spine- 

 bases. 



Keokuk group. Illitwis. 



