PLATE XVIII. 



(Figures 1-5, 11-17, 1'J by U, P. Whitfield ; 6-13, 18 by F. B. Meek.) 



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



s. Septum. a'. Posterior adductors. 



V. Brachial ridges. ^ r. Diductors. 



Genus PRODUCTUS, Sowerby. 



(See Plates XVIIa, and XIX.) 

 Page 3-21. 



Pkoductus Newberryi, Hall. 



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

 cardinal exti'emities. 



Waverly sandstone. MeUina, Ohio. 



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

 the brachial ridges. 



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



Waverly sandstpne. Newark, Ohio. 



Productus, sp. ? coiiip;ii-e Prattenanus, Norwood. 



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

 Waverly sandstone. Newark, Ohio. 



Productus, ? sp. ? 



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



Chemung group. Cattaraugus .county, N.Y. 



Productus FLEMrNGi. Sowerby, var. Burlixgtonensis, Hall. 



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



Bui'lington limestone. Burlington, loxDa. 



Productus mesialis, Hall. 



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



Keokuk group. Nauiioo, Illinois. 



Productus semireticulatus, Martin. 



Fig. 11. A cast of the exterior of a large brachial valve j showing the surface characters. 

 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 cardinal spines on the 

 pedicle-valve. 



Keokuk group. Warsaw, 1 llinois. 



Productus alternatus, Norwood and Pratten. 



with the peculiai' suH 



Keokuk group. Illinois. 



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

 bases. 



