EXPLANATION OF PLATE I. 



Figs. 1-2. LINGULA GORBYI Miller p. 35 



Views of two separate valves. (W. M., Nos. 9653 and 9654.) 

 Choutean limestone, Pettis County, Missouri. 



Fig. 3. LINGULA LOUISIANENSIS n. sp p. 34 



View of a single valve, the holotype. (D. K. G., No. 1901.) 

 Louisiana limestone, Louisiana, Missouri. 



Fig. 4. LINGULA HALLI White p. 35 



View of a single valve, the holotype. (U. M., No. 1691.) 

 Burlington limestone, Burlington, lozva. 



Fig. 5. LINGULA MEMBRANACEA Winchell p. 33 



View of a single valve, the holotype. (U. M., No. 1330.) 

 Chonopectus sandstone, Burlington, Iowa. 



Fig. 6. LINGULA VARSOVIENSIS Worthen p. 36 



View of a single valve, the holotype. (I. S. M., No. 2601.) 

 Warsaw beds, IVarsaiv, Illinois. 



Fig. 7. LINGULA INDIANENSIS Miller & Gurley p. 37 



View of a single valve, the holotype. (W. M., No. 6187.) 

 Crawfordsville shale, Crawfordsville, Indiana. 



Fig. 8. LINGULA sp. 



View of an imperfect valve. (W. M., No. 7885.) 

 Chester group, Chester, Illinois. 



Fig. 9. LINGULA sp. 



View of an imperfect specimen. (W. M., No. 14497.) 

 St. Louis limestone, Monroe County, Illinois. 



Fig. 10. BARROISELLA SUBSPATULATA (Meek & Worthen). 



View of a single, very perfect valve. (W. M., No. 7887.) 

 Devonian black shale, Union County, Illinois. 



Fig. 11. GLOSSINA SEDALIENSIS (Miller) p. 37 



View of an incomplete valve with the outline restored. (W. M., 

 No. 9652.) 



Chouteau limestone, Pettis County, Missouri. 



Fig. 12. GLOSSINA LINEOLATA (Rowley) , p. 38 



View of a single valve, one of the cotypes. (R. R. R.) 

 Louisiana limestone, Louisiana, Missouri. 



Fig. 13. ORBICULOIDEA CAPAX (White) p. 39 



View of the holotype, an imperfect brachial valve. (U. M., No. 

 1331.) 



Chonopectus sandstone, Burlington, Iowa. 



Figs. 14-17. ORBICULOIDEA KEOKUK (Gurley) p. 41 



14-15. Views of the cotypes of the species, a pedicle and a brachial 

 valve. (W. M., No. 6331.) 16-17. Views of two pedicle valves, 

 one external and the other internal. (W. M., No. 14787.) 

 Crawfordsville shale, Crawfordsville, Indiana. 



Fig. 18. ORBICULOIDEA sp. 



View of a very perfect brachial valve. (W. M., No. 12281.) 



Productus magnus bed, Ste. Genevieve County, Missouri. 



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