PRODUCTELLA 



101 



the anterior margin, strongly and rather abruptly compressed towards the 

 cardinal extremities ; mesial sinus obsolete ; beak small and incurved. 



Brachial valve rather deeply concave, with the surface somewhat de- 

 flected towards the cardinal extremities, the concavity rather narrow 

 at the beak and broadening rapidly anteriorly. Internally the cardinal 

 process is rather small, bifid, with each division longitudinally excavated 

 upon its posterior and outer surfaces; from the base of the cardinal pro- 

 cess a pair of ill-defined, low, broadly diverging ridges extend for one- 

 third or more the distance to the postero-lateral margins, their posterior 

 slopes being more abrupt and constituting the rudimentary dental 

 sockets ; a broad, low ridge extends anteriorly along the median line of the 

 valve from the junction of the two diverging ridges, which is soon ab- 

 ruptly constricted to a narrow and low median septum reaching to or 

 beyond the middle of the valve; the brachial impressions of moderate 

 strength, usually reaching a little more than two-thirds the distance from 

 their bases to the lateral and anterior margins ; the inner surface covered 

 throughout, except upon the brachial impressions, the median septum and 

 the region adjacent to the base of the cardinal process, by closely crowded 

 papillae or tubercles, arranged more or less definitely in radiating series. 



Surface of both valves marked by more or less crowded, concentric 

 lines of growth. Spine bases exceedingly variable in their development; 

 on the pedicle valve they are sometimes nearly absent except a few near 

 the cardinal margin, and again they are more or less crowded and usually 

 arranged in radiating series over the entire surface, sometimes they are 

 strong and elongate and the radiate arrangement is so well defined 

 that the surface of the valve appears almost to be marked by radiating 

 costae ; upon the brachial valve the spine bases are never so conspicuous. 



Remarks. This is a highly characteristic species from the Louisiana 

 limestone, and while it is exceedingly variable in some of its features, 

 especially its surface markings, it is so different from other species of our 

 faunas that there can be no difficulty in recognizing it. 



Horizon. Louisiana limestone. 



PRODUCTELLA NUMMULARIS (Winchell) 

 Plate XIX, Figs. 39-41 



1863. Strophalosia f nummularis Winchell, Proc. Acad. Nat. Sci. Phil., 



p. 4. 

 1900. Productella nummularis Weller, Trans. St. Louis Acad. Sci., vol. 10, 



p. 71, pi. 1, figs. 9-10. 



Description Shell of medium size, subcircular in outline, a little wider 

 than long, the hinge-line about two-thirds the width of the shell, the 

 cardinal extremities obtusely subangular or a little rounded. The dimen- 

 sions of an imperfect pedicle valve are: length 27 mm., width 24 mm., 



