152 MISSISSIPPIAN BRACHIOPODA 



sloping with a gently convex curvature to the lateral and anterior mar- 

 gins ; the mesial portion of the valve scarcely or not at all differentiated 

 from the general surface in the umbonal region, in the median portion 

 of the valve and towards the front there is usually a low, ill-defined, 

 rounded, mesial fold bounded by much narrower, equally ill-defined, shal- 

 low furrows, the top of the fold not being raised above the general convex 

 curvature of the valve, near the front margin the median portion of the 

 valve is commonly depressed to a slight degree in a broad, shallow, ill- 

 defined sinus; the beak short and a little incurved; cardinal area small, 

 concavely curved from the base to the apex, the lower, flattened portion 

 sloping posteriorly from the plane of the valve at an angle of about 40 

 degrees, the lateral margins sharply defined, the delthyrium large, much 

 broader than high, its width at the base about one-third, or nearly one- 

 third, the total length of the hinge-line. Internally the cardinal teeth 

 are strong and diverging, originating on either side of the delthyrium 

 from the floor of the valve; the muscular scars are subovate in outline 

 and rather small for this genus, their total length usually being less than 

 one-half the length of the valve ; they are rather deeply impressed, with 

 a raised border, the adductor scars do not reach anteriorly as far as the 

 diductors but in front of them, a distinctly elevated median ridge sepa- 

 rates the two lobes of the diductor scars, the unpaired pedicle muscular 

 scar occupies the rostral portion of the valve and is differentiated from 

 the contiguous scars in front ; beyond the muscular scars the inner surface 

 of the valve is pitted or is covered with faint, anastomosing ridges, and 

 along the lateral and anterior margins it is crenulated, the crenulations 

 corresponding in size with the exterior costse of the valve. 



Brachial valve about equally convex with the pedicle, the greatest 

 convexity a little posterior to the middle, the surface sloping with a 

 gently convex curvature to the lateral and anterior margins, a little com- 

 pressed towards the cardinal extremities ; a shallow, rounded, ill-defined 

 mesial sinus originates in the umbonal region and continues to the anterior 

 margin; the beak small and short, not incurved; cardinal area smaller 

 than that of the opposite valve, its surface lying in nearly the plane of 

 the valve. Internally the cardinal process is rather small and low, 

 rising from the posterior extremity of a rather broad, elevated ridge occu- 

 pying the median line of the interior of the valve and extending anteriorly 

 from the apex of the valve to an ill-defined termination near the anterior 

 margins of the muscular scars ; socket plates strong and widely diverging, 

 resting upon the floor of the valve ; the muscular scars shorter and a little 

 wider than those of the opposite valve ; the lateral and anterior margins 

 of the valve crenulated internally. 



Surface of both valves marked by numerous, uniform, depressed, 

 rounded, radiating costae, which increase by bifurcation and intercalation, 



