150 MISSISSIPPIAN BRACHIOPODA 



near or a little anterior to the middle, the hinge-line less than one-half 

 the greatest width of the shell, the cardinal extremities rounded. The 

 dimensions of two pedicle valves are : length 26.8 mm. and 24 mm., width 

 28.3 mm. and 25 mm., length of hinge-line 10 mm. and 11.8 mm., convexity 

 6.6 mm. and 6 mm. The dimensions of a large brachial valve are : length 

 28 mm., width 31.1 mm., convexity 6.5 mm. 



Pedicle valve most convex posterior to the middle, the umbo rather 

 prominent, the surface sloping abruptly to the cardinal margins, some- 

 times a little compressed towards the cardinal extremities, curving much 

 more gently to the lateral and anterior margins; the mesial portion of 

 the valve broadly and indefinitely flattened anterior to the middle, some- 

 times very slightly sinuate near the front margin ; beak rather prominent ; 

 cardinal area small, concave, with the curvature increasing towards the 

 beak, the lower, flatter portion sloping posteriorly at an angle of about 

 60 degrees to the plane of the valve, the lateral margins sharply defined, 

 the delthyrium large and broadly triangular, its basal width sometimes 

 occupying fully one-third of the total length of the hinge-line. Internally 

 the cardinal teeth are of moderate strength and widely divergent ; the 

 muscular scars are large and flabellate .with a slight raised marginal 

 border, reaching beyond the middle of the valve anteriorly, sometimes 

 being fully two-thirds the total length, with a width of from one-half 

 to two-thirds the total width of the valve, the adductor scars are large 

 and well defined, resting upon a somewhat elevated area near the middle 

 of the entire muscular region which is continued anteriorly to the limits 

 of the diductor scars in a raised median ridge somewhat narrower than 

 the adductor scars themselves, the diductor scars are very large and are 

 marked by several slight, subangular, radiating ridges, the unpaired 

 pedicle muscle scar is large, occupying the entire rostral portion of the 

 valve and is sharply differentiated from the contiguous scars in front; 

 the inner margin of the valve is crenulate anteriorly and laterally. 



Brachial valve subequally convex with the pedicle, the greatest con- 

 vexity near the middle, the surface sloping with a gently convex curvature 

 in all directions, the cardinal extremities sometimes slightly compressed ; 

 the mesial portion of the valve obscurely flattened or sometimes very 

 slightly impressed in an ill-defined sinus ; beak small, not incurved ; car- 

 dinal area small, lying in nearly the plane of the valve. Internally the 

 socket plates are prominent, with their anterior extremities almost crura- 

 like in form ; they rest upon the floor of the valve through almost their 

 entire length and are widely divergent ; the cardinal process is prominent 

 and highly elevated, its posterior surface is nearly vertical and sometimes 

 trilobate towards the apex, the anterior surface slopes obliquely to the 

 floor of the valve and continues as a low, ill-defined mesial ridge to the 

 anterior margins of the muscular scars; muscular scars smaller than 



