192 MISSISSIPPIAN BRACHIOPODA 



median portion of the valve, posteriorly, the surface is regularly convex 

 transversely, but near the postero-lateral margins it curves rather ab- 

 ruptly towards the opposite valve and then continues in a nearly vertical 

 direction to the margin where it meets the similar vertical surface of the 

 opposite valve and forms the lateral flattened or slightly concave region 

 which is present each side of the beak ; the mesial fold is obsolete in the 

 umbonal region, is gradually elevated anteriorly to near the front margin 

 where the elevation becomes abrupt, or rather the lateral slopes are 

 curved abruptly towards the opposite valve, the fold is sharply denned 

 and is nearly flat or slightly convex transversely across the top with ab- 

 ruptly descending sides ; the lateral slopes of the valve are narrow, their 

 surface curves gently from the sides of the fold towards the lateral mar- 

 gins for a short distance and then curves abruptly towards the opposite 

 valve ; the beak is incurved strongly beneath that of the opposite valve ; 

 the plications are similar in form and number to those of the opposite 

 valve, one or more pairs upon the fold sometimes coalescing as they ap- 

 proach the anterior margin. Internally no cardinal process is present 

 and the hinge-plate is divided to the base, each division being supported 

 by one side of a crural cavity which is joined to the floor of the 

 valve by a median septum, the crural cavity continues to a point opposite 

 the articulation of the hinge, beyond which the median septum becomes 

 rapidly lower, the crura extend forward into the cavity of the shell from 

 the anterior margin of the hinge-plate. 



In addition to the plications the surface of each valve is marked by 

 fine radiating stria?, four or five of which occupy the space of one milli- 

 meter, and by still finer concentric striae with stronger lines of growth at 

 intervals. 



Remarks. In some of its aspects this species resembles the elongate, 

 coarsely plicated shells of Rhynchotetra caput-testudinis with its flattened 

 lateral areas on each side of the beak, but it is smaller than that species 

 and more distinctly striated longitudinally besides possessing an entirely 

 different internal structure, there being no median septum and spondy- 

 lium in the pedicle valve. The species differs from P. striaticostatnm in its 

 larger size, more elongate form, more convex valves and the more con- 

 spicuous, lateral, flattened areas on each side of the beak. 



Horizon. Kinderhook. 



Genus PUGNOIDES Weller 



Description. Shells rhynchonelliform, below medium size, subovate in 

 outline, with the fold and sinus well developed. Both valves marked by 

 rounded or subangular plications which become obsolete in the posterior 

 portion of the shell. Internal characters of both valves essentially as in 

 Camarotcechia. 



