EXPLANATION OF PLATE XIII. 



Figs. 1-12. PRODUCTUS ARCUATUS Hall p. 107 



1-3. Pedicle, lateral and posterior views of a very perfect pedicle 

 valve. 4-5. Pedicle and lateral views of a natural mould of 

 the concave brachial valve. (W. M., No. 9823.) 



Chouteau limestone, Choutcau Springs, Missouri. 

 6-8. Pedicle, lateral and posterior views of a very perfect pedicle 

 valve. (W. M., No. 14285.) 9-10. Pedicle and lateral views 

 of a nearly complete specimen. 11-12. Pedicle and lateral 

 views of the natural mould of the concave brachial valve of 

 the same shell. (W. M., No. 14330.) 



Kinderhook oolite, bed No. 6, Burlington, Iowa. 



Figs. 13-17. PRODUCTUS WORTHENI Hall p. 126 



13-15. Pedicle, lateral and posterior views of a nearly perfect 

 pedicle valve. 16. Pedicle view of a natural mould of the 

 external surface of a brachial valve. (W. M., No. 281.) 



Residual chert, Springfield, Missouri. 



17. Pedicle view of a nearly complete natural mould of the ex- 

 ternal surface of a brachial valve. (W. M., No. 294.) 

 Keokuk limestone, near Springfield, Missouri. 



Figs. 18-23. PRODUCTUS MARGINICINCTUS Prout p. 127 



18-19. Pedicle and brachial views of a nearly complete example. 



20-21. Pedicle and lateral views of a nearly complete pedicle 



valve. (W. M., No. 10846.) 22-23. Pedicle and lateral views 



of another nearly complete pedicle valve. (W. M., No. 14290.) 



St. Louis limestone, St. Louis., Missouri. 



Figs. 24-29. PRODUCTUS SCITULUS Meek & Worthen p. 120 



24-26. Pedicle, lateral and posterior views of a nearly complete 

 pedicle valve. (W. M., No. 13128.) 



St. Louis limestone, St. Louis, Missouri. 



27-28. Views of two nearly perfect internal casts of pedicle valves. 

 29. View of the impression of the exterior of a brachial 

 valve. (W. M., No. 14764.) 



St. Louis limestone (chert), Fountain Creek, Monroe 

 County, Illinois. 



Figs. 30-35. PRODUCTUS SAMPSON: Weller p. 129 



30-33. Pedicle, brachial, lateral and posterior views of a nearly 

 perfect shell. The holotype. (W. M., No. 9695.) 



Chouteau limestone, Pettis County, Missouri. 



34-35. Views of two larger pedicle valves. (W. M., No. 4698.) 

 Fern Glen formation, near Kiinmswick, Missouri. 



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