PLATE XXXI. 
(Figures 1-3, 6-10,12,16,18,19 by R. P. Whitfield; 4 , 5,11,13,14,16,17 by P. B. Meek.) 
Leg-end : A. Cardinal area. 
Adt. Denticulated cardinal marg-in. 
Dg. Deltidial grooves, 
s'. Callosity in delthyrium. 
t. Teeth. 
j. Cardinal process, 
b. Dental sockets, 
a. Adductor scars, 
r. Diductor scars. 
Genus SPIRIFER, Sowerby, 
Page 1. 
Spirifee increbescens, Hall. 
See Plate 30. 
Fig. 1. A portion of the interior of the pedicle-valve ; showing the denticulations along the cardinal mar¬ 
gin, the delthyrial callosity and the form of the muscular scar. 
Fig. 2. Corresponding poi-tion of a brachial valve ; showing cardinal process and dental sockets. 
Fig. 3. An enlargement of the cardinal area to show the denticulated cardinal edge of the pedicle-valve. 
The surface of the shell on the area is somewhat exfoliated, exposing the series of vertical 
canals, each of which terminates in a denticle. The margin of the brachial valve shows a series 
of small sockets corresponding to the denticles. 
Chester limestone. Chester, Illinois. 
Spirifer opimus, Hall. 
Figs. 4, 5. Brachial and profile views of a normal individual. 
Coal Measures. Iowa. 
Fig. 6. The interior of. the pedicle-valve ; showing the character of the muscular impression. 
Fig. 7. The interior of a brachial valve. 
Coal Measui-es. Bomjardim, Brazil. 
Spirifer Grimesi, Hall. 
Fig. 8. A cardinal view; showing the high, relatively short area, and the convexity of the valves. 
Fig. 16. Dorsal view of a nearly entire individual of normal mature size. 
Fig. 17. The interior of a portion of the pedicle-valve ; showing the structure of the muscular area. 
Fig. 18. A portion of an internal cast of the pedicle-valve; showing the impressions of the adductor and 
diductor muscular scars. 
Fig. 19. Enlargement of the radiating surface striae. 
Burlington limestone. Burlmgton, Iowa. 
Spirifer Newberryi, sp. nov. 
Fig. 9. The exterior of the brachial valve ; showing the fine plications. 
Fig. 10. An enlargement of the surface ; showing the fine striae. 
Waverly group. Ohio. 
Spirifer imbrex, Hall. 
Fig. 11. The exterior of a brachial valve. 
Fig. 12. An enlargement of the surface; showing the bifurcating plications and the lamellose concentric striae. 
Burlington limestone. Burlington, Iowa. 
Spirifer suBiEQUALis, Hall. 
Figs. 13, 14. Cardinal and dorsal views of the original specimen; showing the imbricated exterior. 
Warsaw limestone. Warsaw, Illinois. 
Spirifer Marionensis, Shumard. 
Fig. 15. A view of a rather small example; showing the fasciculate plications. 
Choteau limestone. Pike county, Missouri. 
