Brachiopoda of the Cincinnati Group. 55 



muscular scars, aud smooth visceral region of the dorsal valve, and 

 termination of the furrows and ridges in the visceral region of the 

 ventral valve, in an oval outline, Avithout extending into the reflected 



margm. 



StropJiomena tenuistriata — (Soweeby, 1839). 



Shell semi-circular, wider than long ; hinge line longer than the 

 breadth of the valves further forward ; lateral extremities acute and 

 sometimes deflected. 



Dorsal valve flat in the cardinal and central regions, and curved ab- 

 ruptly upward on the anterior and lateral margins ; beak very small 

 and projecting slightly beyond the edge of the area, which is sublinear 

 and directed nearly backward. Interior with light, bifid cardinal pro- 

 cess directed obliquely forward and flattened on the posterior faces ; 

 sockets for the reception of the dental ridges of the other valve mod- 

 erately well defined ; dental ridges low and gradually lost in the thick- 

 ened circular elevation surrounding the muscular scars ; narrow ele- 

 vated mesial ridge separating the two circular muscular impressions, 

 which are situated just forward of the cardinal process; bottom of 

 muscular scars marked with longitudinal lines, deepest near the cardi- 

 nal process ; outside the subcircular elevation surrounding the mus- 

 cular scars the surface is granulated and irregularly marked with 

 more or less obscure longitudinal or oblique lines ; anterior and lateral 

 margins abruptly curved or geniculated over an elevated zone, bound- 

 ing the visceral cavity, and marked with transverse obscure lines and 

 granulations. 



Ventral valve convex on the umbo and flattened over the cardinal 

 and central regions, and curved abruptly downward on the anterior 

 and lateral margins ; beak distinct, perforated and projecting a little 

 beyond the edge of the area ; area of moderate height, gradually nar- 

 rowing from the beak toward the extremities, and forming with the 

 area of the other valve an acute angle. Interior with dental ridges 

 divergent, and produced into a subcircular thickening of the shell or 

 elevated ridge surrounding the muscular cavity, except at the opening 

 on the anterior side ; obscure mesial ridge separating the muscular 

 cavity, which is longitudinally aud irregularly lined ; whole interior 

 surface marked with obscure lines and granulations. 



Surface of both valves ornamented with numerous round, i-adiating 

 striae, that increase by intercalation and bifurcation on each valve ; 

 about six strong, concentric wrinkles over the visceral cavity mark each 

 valve, and fine concentric striae may be seen with the aid of a 

 magnifier. 



