18 Brachiopoda of the Cincinnati Group. 



Wiynclionella dentata — (Hall, 1847). 



Shell rather smaller than the medium size in this genus, trigonal- 

 subglobose, generally slightly wider than long, and usually, in adult 

 examples, quite convex ; posterior lateral margins nearly straight, or a 

 little convex in outline, and converging to the beaks at nearly a right 

 angle ; anterior lateral margins rounded or subangular ; front usually a 

 little sinuous, as seen in a direct view of either valve. 



Dorsal valve more convex than the other, particularly in the anterior 

 central region, where it is often very prominent, being elevated in the 

 form of a distinct mesial ridge, that is divided into two plications by a 

 central furrow ; lateral slopes rounding off more or less abruptly, and 

 each occupied by from four to five simple, rather angular, radiating 

 plications ; beak strongly incurved. 



Ventral valve (as seen in a side view) somewhat strongly arched 

 from beak to front, or more or less compressed in the central region, 

 and abruptly curved up at the front and beak ; mesial sinus commenc- 

 ing small near the beak, and widening and deepening (with sloping 

 sides and a single central plication) to the front, where it equals about 

 one half the entire breadth, and terminates a more or less produced, 

 subtrigonal marginal projection, curved up nearly at right angles to 

 the plane of the valve, and fitting into a corresponding sinus in the 

 edge of the same ; lateral slopes generally quite abrupt from the edges 

 of the mesial sinus, and each occupied by about five single subangular 

 plications ; beak incurved, but not so closely upon that of the other as 

 to conceal the small foramen under its apex. 



Surface of both valves with the plications continued to the points of 

 the beaks, and imparting to the interlocking anterior margins, a sharply 

 zigzag outline ; while on well preserved specimens, very fine, obscure 

 lines of growth may be seen, by the aid of a magnifier, crossing the 

 plications and furi'ows between them, parallel to the zigzag anterior 

 and lateral margins ; though these lines are nearly or quite obsolete, 

 excepting near the front. 



Found at Kichmond, Indiana, and at other places in the upper 100 

 feet of the Cincinnati Group, in moderate abundance. The R. capax 

 commences a hundred feet lower, and has passed its turning point of 

 greatest abundance before this species appears in the rocks. 



Family Orthidce (sometimes written Orilmidce). 



Shell transversely oblong, depressed, rarely foraminated ; hinge line 

 wide and straight ; beaks inconspicuous ; valves plano-convex or con- 



