PRODUCTELLA 99 



Pedicle valve gibbous, arched from the umbonal region to the anterior 

 margin with the posterior curvature somewhat more convex than the 

 anterior, the umbonal region prominent and strongly protuberant beyond 

 the hinge-line, the surface curving abruptly to the cardinal margin and 

 less abruptly to the lateral and anterior margins, rather abruptly deflected 

 towards the cardinal extremities to form small, compressed auriculations ; 

 mesial sinus obsolete; the beak strongly incurved. 



Brachial valve moderately concave in its visceral portion, with the 

 cardinal extremities somewhat deflected, anteriorly and laterally the 

 valve is abruptly curved, or subgenieulate in passing from the visceral 

 region to the produced portion of the valve, so that the entire valve be- 

 comes very deeply concave at maturity. 



Surface of both valves usually marked by strong, concentric, wrinkle- 

 like folds in the visceral region, which become inconspicuous or obsolete 

 upon the produced portion of the shell ; surface of the pedicle valve more 

 or less distinctly marked by elongate nodes, especially upon the produced 

 portion of the shell, which are frequently more or less connected longi- 

 tudinally to form rather broad, rounded, depressed, longitudinal costas 

 which are irregular in their development, and not infrequently nearly 

 obsolete ; the brachial valve marked by shallow, more or less elongate de- 

 pressions which are at times connected to form somewhat discontinuous, 

 longitudinal furrows, these markings being more conspicuous upon the 

 produced portion of the valve but being likewise present upon the visceral 

 surface ; they are more constant than the corresponding costee of the 

 pedical valve ; entire surface of both valves marked by fine, concentric 

 lines of growth. 



Remarks. This species was originally described from an external im- 

 pression of a brachial valve from the upper yellow Kinderhook sandstone 

 at Burlington, Iowa. Productella shumardiana was described from two speci- 

 mens, a pedicle valve from the same horizon and locality from which the 

 type of P. c&ncentrica was obtained, and a brachial valve from, the Lou- 

 isiana limestone of Clarksville, Missouri; the first of these specimens is 

 undoubtedly a member of the same species as the type of P. concentrica, 

 while the second specimen is an example of P. pyxidata. Productus 

 cooperensis was described, from- the Chouteau limestone of central Missouri, 

 where it is a common species; many examples of both the brachial and 

 pedicle valves have been examined and they exhibit no characters by 

 means of which they can be separated from P. concentrica. All three of 

 these forms, except one of the type specimens of P. shumardiana must 

 be considered as synonyms, and for this form the namt P. concentrica 

 holds priority. It has sometimes been suggested that the species should 

 be made to include also P. pyxidata, but that species is clearly distinct, 

 P. concentrica being characterized by its narrower form and its much 



