BRACHIOPODA—PROTREMATA. 247 



gin. Brachial valve concave with a very slight mesial fold. Sur- 

 face marked by coarse radiating plications sometimes bifurcating 

 or coalescing and crossed by a few concentric wrinkles. A few 

 strong, scattered spines present on the pedicle valve. 

 Throughout the Upper Carbonic of North America. 



155. P. inflatus McChesney. Upper Carbonic. 

 Very gibbous, subquadrate in outline. Beak small and incurved. 



Sinus broad, shallow and distinct. Much resembles P. semireticu- 

 latus but differs in its smaller size and in the fineness of its radial 

 striae. Concentric wrinkles present in the posterior third. Spines 

 few, distant and large. 

 Indiana and Colorado. 



156. P. longispina Sowerby ? (Fig. 297, /-g\) Upper Carbonic. 

 Small, much wider than long with extended hinge line and 



prominent ears. Pedicle valve gibbous with slightly projecting 

 beak and broad mesial sinus. Brachial valve concave. Surface 

 marked by obscure radiating ribs which are obsolete on the umbo. 

 Spines originally long but usually broken off. 



Throughout the Upper Carbonic of the United States. 



157. P. mexicoanus Shumard. Upper Carbonic. 

 Small. Sides flattened, giving the shell a somewhat four-sided 



outline when viewed from the hinge margin. Pedicle valve 

 strongly arched and without mesial sinus. Surface with 16-20 

 coarse radiating costae on which are scattered spines. 

 Nevada, New Mexico. 



158. P. muricatus Norwood and Pratten. Upper Carbonic. 

 Small, semicircular with breadth exceeding length. Curvature 



moderate. Distinguished by its surface markings, consisting of 

 concentric nodose wrinkles and coarse, somewhat nodose striae. 

 Whole shell covered by small spines. 



Ohio, Illinois, Missouri, Iowa, Colorado, New Mexico. 



1 59. P. nebraskaensis Owen. (Fig. 298, a-c.) 



Upper Carbonic. 



Of medium size. Distinguished by the absence of a distinct 

 sinus in the pedicle valve and by the large number of spines scat- 

 tered over the surface of both valves. (See P. symmetficus.} 



Ohio, Indiana, Illinois, Missouri, Nebraska, Colorado, Nevada, 

 New Mexico, Arizona. 



