62 MISSISSIPPIAN BRACHIOPODA 



Pedicle valve nearly flat throughout in immature specimens, becoming 

 concave as it approaches maturity, the curvature beginning at a little 

 more than two-thirds the length of the shell from the beak in the speci- 

 men whose dimensions are given above, towards the cardinal extremities 

 the surface is very gently convex as it approaches the cardinal margin ; 

 mesial sinus obsolete ; the beak inconspicuous, in the internal casts scarce- 

 ly extended beyond the straight or nearly straight cardinal margin of the 

 valve ; cardinal area narrow, lying at nearly a right angle to the plane of 

 the valve, the lateral margins angular, the two sides of the beak being in 

 nearly a straight line ; the delthyrium broadly triangular. Internally 

 the hinge-teeth are supported by thickened ridges on the inner surface 

 along each margin of the delthyrium, which can scarcely be designated as 

 dental plates ; the muscular scars obscure or poorly defined. 



Brachial valve rather strongly convex, the greatest convexity posterior 

 to the middle, the surface curving more abruptly towards the cardinal 

 margin, the cardinal extremities compressed and subauriculate, the um- 

 bonal region prominent and projecting somewhat beyond the cardinal 

 margin ; the mesial portion of the valve flattened or depressed in a shal- 

 low, ill-defined sinus which in the casts is better developed near the beak ; 

 the beak not conspicuous, somewhat incurved. Internal characters not 

 well exhibited in any of the specimens. 



Surface of both valves marked by radiating costa3 which, on the casts, 

 are subangular and irregular in size, although not distinctly alternating, 

 those of the pedicle valve being more regular than those of the brachial, 

 from two to four occupying the space of 1 mm. at the margin of the 

 valves; the costa? are apparently more numerous at the margin than fur- 

 ther back, the additional ones being added close to the margin and being 

 in the nature of crenulations of the inner margin which would not be 

 shown on the external surface, rarely more than two in the space of 1 mm. 

 at the margin on the outside. The costae are crossed by concentric lines 

 of growth which are usually restricted to the region near the margin. 



Remarks. This species is known only from specimens preserved as in- 

 ternal casts in a fine-grained yellow sandstone, which do not preserve the 

 minute surface markings. In no case have the two valves been seen in 

 articulation, but the pedicle and brachial valves here described occur in 

 such association as to make it almost certain that they are parts of the 

 same species. The species is especially characterized by the slight mesial 

 sinus in the brachial valve, by the flatness of the pedicle valve to near the 

 margin where the concavity begins, and by the straight cardinal margin 

 of the pedicle valve and narrow cardinal area. 



Horizon. Kinderhook. 



