128 MISSISSIPPIAN BRACHIOPODA 



the radiating costa? in the posterior half of the shell, there are distinct, 

 rounded, wrinkle-like concentric markings, which are stronger towards 

 the cardinal extremities, and the entire surface is covered by exceed- 

 ingly fine, concentric markings, which are stronger in the intercostal 

 furrows. 



Brachial valve nearly flat throughout the greater portion of its area, 

 but curving rather abruptly towards the lateral and anterior margins 

 and continuing for a short distance nearly in contact with the inner 

 surface of the opposite valve; the flattened portion of the valve is 

 gently concave towards the beak, with a rather broad, slightly elevated 

 region extending obliquely from each side of the beak to the lateral 

 margins a little in front of the cardinal extremities, the auriculations 

 flattened. Surface of the valve marked by rounded, radiating costae 

 somewhat more depressed than those of the opposite valve, which in- 

 crease by bifurcation and intercalation; the costse are crossed by finer, 

 concentric, wrinkle-like markings which give to nearly the entire surface 

 a semireticulate appearance, and also by much finer concentric mark- 

 ings similar to those of the opposite valve; at the intersection of the 

 stronger radiating and concentric markings, especially towards the 

 anterior margin of the valve, are slight nodes which are apparently the 

 bases of spines. 



Remarks. This is one of the most distinct species of the genus 

 Productus in our faunas, and may be recognized always by the very con- 

 spicuous, ring-like inflation about the lateral and anterior margins of 

 the pedicle valve. The only other species among those here recognized 

 possessing a character at all similar to this one, is P. wortheni, but in P. 

 marginicinctus the feature is very nrach more conspicuously developed. 

 Both these species are peculiar in the form of the brachial valve, which 

 is so nearly flat throughout the greater portion of its surface with the 

 rather abrupt geniculation near the lateral and anterior margins. 



Horizon. St. Louis limestone. 



PRODUCTUS PARVULUS Winchell 

 Plate XIV, Figs. 24-25 



1863. Producta parvula Winchell, Proc. Acad. Nat. Sci. Phil., p. 4. 

 1901. Productus parvulus Weller, Trans. St. Louis Acad. -Sci., vol. 11, p. 

 160, pi. 14, figs. 21-22. 



Description. Shell very small, longer than wide, the hinge-line equaling 

 or a little shorter than the greatest width. The dimensions of two speci- 

 mens, co-types, are : length from hinge-line to front margin 8 mm. and 6 

 mm., length from umbonal region to front margin 9.1 mm. and 6.9 mm., 

 greatest width 8.4 mm. and 6.3 mm., length of hinge-line 8 mm. and 6.3 

 mm., convexity 5 mm. and 3 mm. 



