136 MISSISSIPPIAN BRACHIOPODA 



Remarks. Among the productoid genera D'iaphragmus has its closest 

 relative in Marginifera. In Marginifera, however, the visceral portion of 

 the brachial valve is surrounded by a ridge-like elevation which rises 

 vertically from the inner surface of the valve instead of continuing in 

 the same plane, as is the condition in Diaphragmus. Marginifera has 

 not as yet been recognized in any of the Mississippian faunas, its earliest 

 appearance being in the Pennsylvanian, while Diaphragmus occurs only 

 in the later Mississippian, so far as it is known at present, and is rep- 

 resented by a single species. 



4 



DIAPHRAGMUS ELEGANS (Norwood and Pratten) 

 Plate XII, Figs. 8-17 



1855. Productus elegans Norwood and Pratten, Jour. Acad. Nat. Sci. 



Phil. (2), vol. 3, p. 3, pi. 1, figs. 7a-c. 

 1855. Productus flexistria Norwood and Pratten, Jour. Acad. Nat. Sci. 



Phil. (2), vol. 3, p. 6. 



1860. Productus fasciculatus McChesney, Desc. New Pal. Foss., p. 38. 

 1860. Productus Cestriensis Worthen, Trans. St. Louis Acad. Sci., vol. 1, 



p. 570. 

 1877. Productus elegans Hall and Whitfield, U. S. Geol. Expl. 40th Par., 



vol. 4, p. 268, pi. 5, figs. 3, 4. 

 1891. Productus elegans Whitfield, Ann. N. Y. Acad. Sci., vol. 5, p. 581, 



pi. 13, figs. 15, 16. 



1894. Productus cestriensis Keyes, Mo. Geol. Surv., vol. 5, p. 44. 



1895. Productus elegans Whitfield, Geol. Surv. Ohio, vol. 7, p. 669, pi. 9, 



figs. 15, 16. 



1897. Productus cestriensis Weller, Trans. Nl Y. Acad. Sci., vol. 16, p. 

 256, pi. 18, figs. 7-9. 



1909. Productus fasciculatus Bassler, Va. Geol. Surv., Bull. No. II A, 



pi. 29, figs. 12, 13. 



1910. Diaphragmus elegans Girty, Ann. N. Y. Acad. Sci., vol. 20, p. 217. 



1911. Diaphragmus elegans Girty, Bull. U. S. Geol. Survey No. 439, p. 51, 



pi. 4, figs. 4-5 



1911. Productus cestriensis Morse, Proc. Ohio State Acad. Sci., vol. 5. 

 p. 372, figs. 9a-g. 



Description. Shell usually below medium size, longer than wide, the 

 greatest width near the mid-length, the hinge-line shorter than the great- 

 est width. The dimensions of a pedicle valve of about average size are : 

 length from hinge-line to front margin 17 mm., length from umbonal re- 

 gion to front margin 22 mm., greatest width 21.8 mm., length of hinge- 

 line 17 mm., convexity of pedicle valve 14 mm. 



Pedicle valve gibbous, the umbonal region protuberant posteriorly be- 

 yond the cardinal margin, the surface dropping nearly vertically to the 

 cardinal margins, curving abruptly to the lateral and anterior margins, 

 compressed at the cardinal extremities into rather small, flattened auricu- 

 lations ; mesial portion of the valve usually broadly flattened from the 



