PLATE XVin. 



(Figures 1-5, 11-17, 19 by K. P. Whitfield; 6-13, 18 by F. B. Mebk.) 

 Legend, j. Caidiiml process. a. Anterior ailductoi's. 



s. Septum. a'. Posterior adductors. 



V. Brachial ridges. ^ r. Diductors. 



Genus PRODUCTUS. Sowekby. 



(See Plates XVIIa, and XIX.) 

 Page 3-21. 



Productus Newberryi, Hall. 



Fig. 1. The exterior of a pedicle-valve; showing the numei-ous spine-bases and lu^tainiiif,-- the sjiines at the 

 cardinal extremities. 



Waverly sandstone. MeUiiia, Ohio. 

 Fig. 2. An internal cast of the united valves ; showing the mu.sculai- impressions of th(! brachial valve and 



the bi'achial ridges. 

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



Waverly sandstone. Newark, Ohio. 



Produotus, sp. ? compare Prattenanus, Norwood. 



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

 Waverly sandstone. Newark, Ohio. 



Productus, ? sp. ? 



Fig. 5. Profile of a pedicle-valve, with spiniferous custae. 



Chemung group. Cattaraugus county, N. Y. 



Productus Flemingi. Soweiljy, var. Burli.vgtonensis, Hall. 



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



Burlington limestone. Burlington, Iowa. 



Productus mesialis, Hall. 



Figs. 9, It). Two views of a pedicle-valve. 



Keokuk gi'oup. Naiivoo, Illinois. 



Productus srmireticulatus, Marl in. 



Fig. 11. A cast of the exterior of a laige brachial valve ; showing the surface charactei's. 

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



Fig. 13. A view of a specimen having the valves united and retaining some of the cai-diiial spines on the 

 pedicle-valve. 



Keokuk group. Warsaw, Illinois. 



Productus alternatus, Norwood and Prattcn. 



with the peculiai' sur: 

 Keokuk grouj). Illhuiis. 



Fig. 14. A pedicle-valve with the peculiai- surface markings, which are due to the exfoliation of the siiiue- 

 bases. 



