EXPLANATION OF PLATE XVIII. 



FigS. 1-6. ECHINOCONCHUS GENEVIEVENSIS II. sp p. 139 



1-2. Pedicle and posterior views of a pedicle valve. 3-4. Pedicle 

 and lateral views of another specimen. (W. M., No. 14767.) 

 Ste. Genevieve limestone, 2 mi. N. E. Columbia, Illinois. 

 5. The impression of the external surface of a brachial valve. 

 6. View of a small pedicle valve. (W. M., No. 14768.) 

 Ste. Genevieve limestone, Columbia, Illinois. 



Figs. 7-10. PRODUCTUS INDIANENSIS Hall p. 131 



7-8. Views of two brachial valves, natural size. 9-10. Pedicle 

 and lateral views of the specimen illustrated in Fig. 7 (x 4). 

 CW. M., No. 14325.) 



Salem limestone, Spergen Hill, Indiana. 



Figs. 11-12. PRODUCTUS sp. 



External and internal views of a free brachial valve. (W. M., 

 No. 7864.) 



Salem limestone (f), Jersey County, Illinois. 



Figs. 13-15. ECHINOCONCHUS MORBILLIANUS (Winchell) p. 142 



Pedicle, lateral and posterior views of the holotype. (U. M., 

 No. 2002.) 



Base of Burlington limestone, Burlington, Iowa. 



Fig. 16. PRODUCTUS sp. 



One of the specimens associated with the type of Echinoconchus 

 morbillianus by Winchell, but clearly not a member of the same 

 species. (U. M., No. 2003.) 



Chonopectus limestone, Burlington, Iowa. 



Figs. 17-18. STROPHALOSIA KEOKUK Beecher p. 145 



A specimen of usual size attached to a shell of Platyceras. 

 18. The same (x 4). (W. M., No. 13008.) 

 Kcokuk limestone, Crawfordsville, Indiana. 



Figs. 19-23. STROPHALOSIA SCINTILLA Beecher '.p. 144 



19-20. Specimens of usual size attached to the shells of Product- 



ella pyxidata. (W. M., No. 6701.) 21. Another similar 



specimen. (W. M., No. 13048.) 22. An enlargement of 



Fig. 20 to x 4. 23. A similar enlargement of Fig. 21 to x 4. 



Louisiana limestone, Louisiana, Missouri. 



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