166 MISSISSIPPIAN BRACHIOPODA 



shell, the hinge-line a little more than one^half the width of the shell, 

 the cardinal extremities rounded. The dimensions of a nearly complete, 

 somewhat crushed specimen, are: length of pedicle valve approximately 

 30 mm., length of brachial valve approximately 30 mm., greatest width 

 36.5 mm., length of hinge-line 20 mm., thickness 23 mm., convexity of 

 pedicle valve 8.2 mm., height of cardinal area 4 mm. The dimensions of 

 another nearly perfect but somewhat unsymmetrical specimen are : length 

 of pedicle valve 28 mm., length of brachial valve 28.3 mm., greatest width 

 32.1 mm., thickness 19.2 mm , length of hinge-line 18.5 mm. 



Pedicle valve much less convex than the brachial, most prominent on 

 the umbo, the surface sloping rather abruptly to the cardinal margin, 

 and more gently to the lateral and antero-lateral margins, compressed 

 towards the cardinal extremities ; the mesial portion of the valve slightly 

 flattened in the posterior portion, becoming impressed anteriorly in a 

 distinct, rounded mesial sinus of moderate depth; the beak moderately 

 prominent and a little incurved ; cardinal area of moderate size, its lateral 

 margins well defined, its surface concave with the curvature increasing 

 towards the beak, the lower flattened portion with a slight posterior slope 

 from the hinge-line ; the delthyrium of moderate size, about as wide as high. 

 Internally the cardinal teeth are supported by short dental lamellae which 

 are continued anteriorly along the inner surface of the valve as elevated 

 ridges along the lateral margins of the muscular scar; muscular scar 

 subcordate in outline with an angular emargination in front, less than 

 one-half the total length of the valve, divided longitudinally by a strong, 

 subangular, median ridge which is highest in front opposite the emargina- 

 tion of the muscular region, gradually decreasing in prominence pos- 

 teriorly. 



The brachial valve much more strongly convex than the pedicle, most 

 prominent near the middle, the surface curving abruptly to the margin 

 in all directions, slightly compressed towards the cardinal extremities, 

 the umbo prominent and projecting conspicuously backward beyond the 

 hinge-line ; the mesial portion of the valve slightly differentiated an- 

 teriorly in a low, rounded, ill-defined mesial fold; beak pointed, much 

 more strongly incurved than that of the opposite valve; cardinal area 

 about one-half as wide as that of the pedicle valve, concave, its lateral 

 margins sharply defined, its inferior portion lying in nearly the plane of 

 the valve and towards the apex curving towards the beak of the opposite 

 valve. Internal characters not observed. 



Surface of each valve marked by fine, rounded, nearly uniform, radiat- 

 ing costae which increase by bifurcation and intercalation, about three 

 costas occupy the space of one millimeter, the intervening furrows about 

 equaling the costas in width ; crossing the radiating costag there are numer- 

 ous, regular, concentric lines of growth which become stronger and more 



