126 MISSISSIPPIAN BRACHIOPODA 



PRODUCTUS WORTHENI Hall 

 Plate XIII, Figs. 13-17 



1858. ProduCrtus wortheni Hall, Geol. Iowa, vol. 1, pt. 2, p. 635, pi. 19, 

 figs. la-b. 



Description. Shell of medium size or smaller, usually broader than long, 

 the hinge-line about equaling the greatest width. The dimensions of a 

 nearly complete pedicle valve are : length from hinge-line to front 

 margin 19 mm., length from umbonal region to front margin 21.4 mm., 

 width 24 mm., convexity 15.5 mm. 



Pedicle valve gibbous, the umbonal region prominent and protuberant 

 beyond the hinge-line, the surface curving abruptly towards the margins, 

 depressed at the cardinal extremities to form flattened auriculations of 

 moderate size, along the lateral and anterior margins a slight, inflated, 

 ring-like border is developed; beak pointed and slightly incurved; 

 mesial sinus obsolete, although the mesial portion of the valve is some- 

 times distinctly flattened. Surface marked by rather fine, rounded or 

 subangular, radiating costaa which increase usually by bifurcation on 

 the posterior portion of the valve, and usually continue across the an- 

 terior slope without further division, becoming more or less discontinu- 

 ous upon the slightly inflated marginal border ; about three costae occupy 

 the space of two millimeters in front, becoming finer towards the car- 

 dinal extremities; the posterior portion of the valve is crossed also 

 by more or less inconspicuous, wrinkle-like, concentric markings which 

 become stronger towards the cardinal extremities; spine bases occur 

 rather sparsely scattered upon the anterior slope of the valve, becoming 

 more crowded and finer upon the marginal border, a group of rather 

 closely crowded spine bases also occupies the greater portion of the 

 surface of the auriculations. Internal characters of the valve not 

 observed. 



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

 becoming abruptly deflected near the lateral and anterior margins and 

 continuing in contact with the opposite valve, the flattened portion of the 

 valve is a little concave at the beak with a rather broad and low ill- 

 defined elevation extending obliquely from each side of the beak towards 

 the lateral margins, outside of which the auriculations are not sharply 

 differentiated. Surface of the valve marked by radiating costae similar 

 to those of the opposite valve, and by concentric, wrinkle-like markings 

 which are more conspicuous than those of the opposite valve ; spine bases 

 are rare upon the greater portion of the surface, but become abundant 

 upon the deflected marginal border and upon the auriculations. In- 

 ternally the cardinal process extends posteriorly from the hinge-line 

 into the umbonal cavity of the opposite valve; anteriorly from the base 



