422 MISSISSIPPIAN BRACHIOPODA 



the more conspicuous mesial depression along the median line of the fold 

 of the brachial valve. 



Horizon. Chester group, Okaw limestone. 



MARTINIA SULCATA n. sp. 

 Plate LXXV, Figs. 11-14 



Description-. Shell below medium size broadly subovate in outline, 

 wider than long, the greatest width near the mid-length, the hinge-line 

 much shorter than the greatest width, the cardinal extremities rounded. 

 The dimensions of a nearly complete specimen are : length of pedicle valve 

 21.4 mm., length of brachial valve 18.5 mm., greatest width 22.5 mm., 

 length of hinge-line 9.5 mm., thickness 13.3 mm. 



Pedicle valve strongly convex, the surface curving abruptly to the car- 

 dinal margin and somewhat more gently to the lateral and anterior mar- 

 gins, not compressed towards the cardinal extremities ; the beak short and 

 blunt rather strongly incurved ; cardinal area small with lateral margins 

 not sharply defined, its surface curving into that of the lateral slopes of 

 the valve without interruption, the delthyrium about as wide as high ; 

 mesial sinus obsolete at the beak and in the umbonal region, originating 

 posterior to the middle of the valve and rapidly deepening anteriorly, be- 

 coming very profound and subangular in the bottom towards the front, 

 arid moderately produced as an anterior extension of the valve, not 

 sharply defined laterally ; lateral slopes regularly convex. 



Brachial valve usually a little less convex than the pedicle, the greatest 

 depth near and anterior to the middle of the valve, the surface curving 

 more abruptly to the cardinal margin, gently convex to the lateral mar- 

 gins, the median line from the beak to the front is convex posteriorly, 

 becoming nearly straight in the central portion and in full grown shells 

 continuing straight to the front or more often becoming a little concave ; 

 the umbonal region not prominent ; the beak small and inconspicuous ; 

 the mesial fold obsolete in the posterior half of the valve but becoming 

 rather strongly elevated in front where it is broadly rounded and ill- 

 defined laterally. 



The surface of both valves marked by very fine and inconspicuous radi- 

 ating markings which can usually be seen only with difficulty, also by ex- 

 ceedingly fine and inconspicuous concentric lines of growth. Both these 

 sets of markings are so faint that the surface appears to be perfectly 

 smooth except upon close examination. 



Remarks. This species differs from M. contracta in its proportionally 

 shorter and broader form, its much more profound mesial sinus towards 

 the front of the pedicle valve, and in the less conspicuous radiating mark- 

 ings of the shell. 



Horizon. Chester group. 



