196 



MISSISSIPPIAN BRACHIOPODA 



Brachial valve strongly convex transversely and moderately convex 

 from the beak to near the front along the median line, the greatest con- 

 vexity of the valve near the front margin, the anterior slope very short 

 and curving somewhat abruptly to the anterior margin; mesial fold not 

 differentiated from the general convexity except towards the anterior 

 margin, and even there the differentiation is not conspicuous; the beak 

 pointed and incurved beneath the beak of the opposite valve ; three short 

 but rather strong plications are present anteriorly upon the mesial fold, 

 and one or two fainter and even shorter ones upon each lateral slope, 



FIG. 10. A series of six cross-sections of the rostral portion of the shell of 

 Pugnoides boonensis (X 2%), showing the dental lamellae and slight median 

 septum of the pedicle valve, and the median septum, the small crural cavity 

 and the crura of the brachial valve. 



the greater portion of the valve posteriorly entirely non-plicate. In- 

 ternally a well developed median septum is present which extends an- 

 teriorly upon the interior surface of the valve for more than one-third 

 the length of the valve, in the rostral portion of the valve the median 

 septum is divided internally to form a crural cavity such as is present in 

 this genus, the crural cavity is very short and terminates posterior to the 

 articulations of the valves, the crural bases joined to the hinge-plate for a 

 short distance beyond the termination of the crural cavity. 



Surface of both valves marked by fine, obscure, but rather regular, 

 concentric lines of growth, with an occasional stronger and more or less 

 conspicuous one; radiating striae not present. 



Remarks. This species approaches the European Pugnax pugnus more 

 nearly in its external form than any other of our American Mississippian 

 rhynchonelloids, but the internal characters of the shell differentiate it 



