104 MISSISSIPPIAN BRACHIOPODA 



umbonal cavity of the opposite valve. Surface of both valves marked by 

 distinct, subequal, regular or flexuose, and usually continuous radiating 

 costae, and by concentric undulations or wrinkles which are commonly 

 restricted to the posterior portion of the valves or to the region towards 

 the cardinal extremities. More or less elongate, hollow spines are pres- 

 ent in various situations upon the shell surface, usually most conspicu- 

 ously developed in the region of the cardinal extremities. 



Remarks. The genus Productus includes one of the largest groups 

 of species of any genus of Mississippian brachiopods, and, as heretofore 

 commonly interpreted, has been made to include several more or less 

 widely diverse types of shells. One of these subordinate groups of 

 species, that typified by P. biseriatus and P. punctatus, has been separ- 

 ated from Productus in the present report as a distinct genus under the 

 name Echinoconchus. Still another subordinate group, of which P. cora 

 is a typical representative, might also, perhaps, be made to constitute a 

 distinct genus, although that has not been done here. Recently one of 

 our species, P. elegans, has been made the type of still another genus, 

 Diaphragmus, by Girty. 



PRODUCTUS BURLINGTONENSIS Hall 

 Plate IX, Figs. 1-10 



1858. Productus flemingi var. burling tonensis Hall, Geol. Iowa, vol. 1, 



pt. 2, p. 598, pi. 12, figs. 3a-g. 

 1883. Productus Flemingi var. Eurlingtoneiisis Hall, Rep. N. Y. State 



Geol. for 1882, pi. (18) 49, figs. 6-8. 

 1892. Productus Flemingi var. Burlingtonensis Hall and Clarke, Pal. 



N. Y., vol. 8, pt. 1, pi. 18, figs. 6-8. 

 1894. Productus burlingtonensis Keyes, Mo. Geol Surv., vol. 5, p. 41. 



Description. Shell of medium size or somewhat larger, broader than 

 long, the hinge-line equaling or greater than the greatest width of the 

 body of the shell, the lateral margins sinuate in front of the cardinal ex- 

 tremities, convexly rounding anteriorly into the anterior margin which is 

 sinuate in its central portion. The dimensions of a nearly complete 

 pedicle valve are: length from the hinge-line to the anterior margin 24 

 mm., length from the umbonal region to the anterior margin 33 mm., 

 length of hinge-line 41.5 mm., width of body of shell at its mid-length 36 

 mm., convexity of pedicle valve 25 mm. 



Pedicle valve strongly ventricose, the umbonal region protruding con- 

 spicuously posteriorly beyond the hinge-line, the beak strongly incurved 

 so that it lies nearly opposite the center of the valve, the surface curving 

 abruptly to the cardinal and lateral margins and a little more gently to 

 the anterior margin, auriculate at the cardinal extremities, the auricula- 

 tions of moderate size and rather abruptly differentiated from the body of 

 the valve, their surface convex antero-posteriorly with the curvature 



