EXPLANATION OF PLATE XXVII. 



Figs. 1-6. RHYNCHOTETRA CAPUT-TESTUDINIS (White) p. 206 



1-4. Pedicle, brachial, lateral and anterior views of the holotype. 

 (U. M., No. 1376.) 



Base of Burlington limestone, Burlington, Iowa. 

 5. View of an incomplete internal cast of a pedicle valve. 6. View 

 of an incomplete internal cast of a brachial valve. (U. M., 

 No. 1376.) 



Kinder ho ok, Bed No. 7, Burlington, Iowa. 



Figs. 7-15. RHYNCHOTETRA GIBBOSUM (Greger) p. 211 



7-10. Lateral, pedicle, brachial and anterior views of a very perfect, 

 small specimen. Cotype. (D. K. G., No. 3602.) 



Burlington limestone, Hannibal, Missouri. 



11-13. Pedicle, brachial and lateral views of a nearly perfect, large 

 specimen. Cotype. (D. K. G., No. 3702.) 



Burlington limestone, Louisiana, Missouri. 



14-15. Views of two imperfect brachial valves. (VV. M., No. 9715.) 

 Burlington limestone, Marion County, Missouri. 



Figs. 16-20. RHYNCHOTETRA OVATUM (Greger) p. 208 



16-17. Pedicle and brachial views of a nearly perfect shell. 

 18-20. Pedicle, brachial and lateral views of another specimen. 

 Cotypes. (D. K. G., No. 3802.) 



Chouteau limestone, Kicsenger Bluff, Warsaw, Benton 

 County, Missouri. 



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