EXPLANATION OF PLATE XLII. 



Figs. 1-3. SPIRIFER FORBESI Norwood and Pratten p. 331 



Pedicle, brachial and posterior views of a nearly perfect specimen 

 probably belonging to this species. (R. R. R.) 

 Burlington white chert, Louisiana, Missouri. 



Figs. 4-16. SPIRIFER TENUICOSTATUS Hall p. 328 



4. View of a pedicle valve. 5-9. Pedicle, brachial, anterior, poste- 

 rior and lateral views of a nearly perfect specimen. Cotypes. 

 (A. M. N. H., No. 51211 & 2.) 



Warsaw formation, Dallas and Warsaw, Illinois. 

 10-13. Pedicle, brachial, posterior and anterior views of a some- 

 what distorted specimen. (W. M., No. 7506.) 



Keokuk limestone, Bentonsport, Iowa. 



14-16. Lateral, pedicle and brachial views of a somewhat crushed 

 specimen. (W. M., No. 7505.) 



Warsaiv formation, Warsaw, Illinois. 



Figs. 17-21. SPIRIFER JEFFERSONENSIS Weller p. 369 



17-18. Pedicle and posterior views of an incomplete pedicle valve. 

 19-21. Views of three brachial valves. Cotypes. (W. M., No. 

 11350.) 



Glen Park limestone, Glen Park, Missouri. 



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