PLATE XXXII. 



(Fixaras 1-S, 7-10, 11-U by K. P. Whitfield; <-6, 11 by F. B. Hbbk.) 



Lagend: A- Delthyiium. a. Anterior adductors, 



t. Teeth. a'. Posteinor adductors, 



a. Deltbyrial callosity. r. Diductors. 



Genus SPIRIFER, Sowerby. 



Page 1. 



Spirifer lateralis, Hall. 



Dorsal view of a large and rather convex individual. 

 Front or marginal view of the same specimen. 



An enlargement of the surface ; showing the pustulose strite on the plications. 

 Warsaw limestone. Warsaw, Illinois. 



Spirifer tenuimarginatus, Hall. 



Figs. 4, 6. Views of an individual of normal size. 



Eeokuk group. Keokuk, Iowa. 



Spirifer rostellatus, Hall. 



Fig. 6. A dorsal view of the origfinal specimen. , 



Keokuk group. Skunk River, Iowa. 



Spirifer Loqani, Hall. 



Fig. 7. A dorsal view of the original s^iecimen ; showing the great size and general external characters 

 of the species. 



Fig. 8. The interior of a portion of the pedicle-valve ; showing the articulating apparatus and the adduc- 

 tor and diductor muaculars scars. 



Keokuk limestone. Near Nauvoo, Illinois. 



Spirifer cameratus, Morton. 



Fig. 9. A large individual ; showing the usual angular fasciculation of the plications. 



Fig. 10. Front view of the same specimen ; showing the relative size of fold and sinus. 

 Coal Measures. Missouri. 



Rg. 11. An individual with broad, low fascicles composed of rounded plications. The bi'eadth of the 

 fascicles is somewhat unusual. 

 Coal Measures. Iowa. 



Fig. 12. An example with the fascicles reduced to sharp, coarse, angular, bifurcating plications. This form 

 and that represented in 6g. 11, indicate the exti-emes of variation in exterior in this species. 



Fig. 13. An enlargement of a portion of the intei-nal cast of the brachial valve ; showing the narrow mus- 

 cular impression and the anterior and posterior adductor scars. 



Fig. 14. An enlargement of a similar portion of a cast of the pedicle- valve ; showing the composition of the 

 muscular area. 



Fig. 15. An enlargement of the surface ornamentation. The surface is marked by exti-emely fine concentric 

 striae, which are minutely papillose. Distinct imbricating lines of growth supervene towards 

 the anterior margin. 



Coal Measures. Ohio and Illinois. _ 



