EXPLANATION OF PLATE XI. 



Figs. 1-5. PRODUCTUS TENUICOSTUS Hall p. 119 



1-3. Pedicle, lateral and posterior views of a good pedicle valve. 

 (W. M., No. 14283.) 



St. Louis limestone, Alton, Illinois. 



4-5. Pedicle and lateral views of another pedicle valve. (W. M., 

 No. 14284.) 



St. Louis limestone, Milan, Illinois. 



Figs. 6-11. PRODUCTUS VIMINALIS White p. 114 



6. Pedicle view of the holotype, a somewhat crushed pedicle 

 valve. 9-10. Pedicle and lateral views of a large pedicle valve, 

 an authentic specimen associated with the holotype in the White 

 Collection at the University of Michigan. (U. M., No. 1693.) 



Burlington limestone, Burlington, Iowa. 



9-10. Pedicle and lateral views of a nearly perfect and undistorted 

 pedicle valve. (W. M., No. 14291.) 



Burlington limestone, Quincy, Illinois. 



11. View of a natural mould of the external surface of the 

 brachial valve, with a portion of the valve, including the 

 cardinal process, adhering posteriorly. (W. M., No. 7925.) 



Burlington limestone, Springfield, Missouri. 



Figs. 12-16. PRODUCTUS MESICOSTALIS n. sp p. 114 



12. View of a pedicle valve. 13-15. Pedicle, posterior and 

 lateral views of a pedicle valve. 16. Interior view of a bra- 

 chial valve. (W M., No. 10585.) 



English River grit, Maple Mill, Washington County, Iowa. 



28 



