PLATE XXXI. 



(FigureB 1-3, 6-10, 12, 15, 18, 19 by 11. P. Whitfield; 4,5, 11, 13, U, Hi, 17 l)y K. B. Meek.) 



Legend : A. Cardinal area. j. Cardinal process. 



Adt. Denticulat(!d cardinal margin. b. Dental sockets. 



D{f. Deltidial grooves. a. Adductor scars. 



s'. Callosity in delthyriiim. r. Diductor scars. 

 t. Teeth. 



Genus SPIKIFEK, Sowerby. 



Page 1. 



Spikifer increbescens, Hall. 



See Plate 30. 

 Fig. 1. A portion of the interior of the pedicle-valve ; showing the denticulatioiis along the cardinal mar- 

 gin, the delthyrial callosity and the form of the muscular scar. 

 Fig. 2. Corresponding portion 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, lUbwis. 



Sfirifek opimus, Hull. 



Figs. 4, 5. Bi'achial 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 Measures. Bomjardim, Brazil. 



Spirifer Grim ESI, Hall. 



Fig. 8. A cardinal view ; showing the high, relatively short area, and the convexity of the valves. 



Fig. 16. Dors.al 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 impre.ssions of the adductor and 



liiductor muscular scars. 

 Fig. 19. Enlargement of the radiating surface stris. 



Bui-lington limestone. Burlington, Iowa. 



Spihifer Newberryi, s[). 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. Oliio. 



Spirifee 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 sub^qualis, Hall. 



Figs. 13, 14. Cardinal and dorsal views of the original specimen ; showing the imbricated exterior. 

 Warsaw limestone. Warsaw, Illinois. 



Spirifer Marionensis, Shuniaid. 



Fig. 15. A view of a rathei' small example ; showing the fasciculate plications. 

 Choteau limestone. Pike comity, Missouri. 



