BBACHIOPODS. 101 



valve ; degree of elevation varying according to the age of the 

 shell; beak incurved, pointed; mesial ridge obscure, with from 

 two to three obscure rounded folds, commencing a short dis- 

 tance in advance of the beak and becoming more prominent 

 toward the front, where the valve is emarginate, and presents 

 two or three deep indentations. Dorsal valve slightly convex 

 near the beak, nearly plain anteriorly ; sinus broad and shallow 

 in young examples, becoming deeper in the more advanced 

 ages of the shell; it has two or three wide obscure plaits, 

 sometimes reaching the beak. Tongue of sinu.s quadrangular, 

 bent upward at right angles to the plane of the valve, and in 

 most specimens equal in length to one-third the length of the 

 shell. The cardinal line in sinuous. The surface of the valves 

 is covered with very fine concentric, imbricating waved lines 

 of growth. (Shumard). 



Horizon and localities. Lower Carboniferous, Chouteau 

 (Upper Kinderhook) limestone: Yandever Falls (Cooper 

 county ), Providence ( Boone county ). 



Rhynchonella cooperensis SHDMARD. 



Rhynchondla cooperensis Shumard, 1855: Geol. Sur. Missouri, Ann. Rep., 

 p. 204, pi. C, figs. 4a-c. 



A form like the immature R. capax, but much broader, and 

 larger and with more rounding, radiating costae. 



Horizon and localities. Lower Carboniferous, Chouteau 

 ( Upper Kinderhook) limestone : Providence ( Boone county ). 



Rhynchonella boonensis SHUMARD. 



Rhynchonella boonensis Shumard, 1855: Geol. Sur. Missouri, Ann. Rep., 

 p. 205, pi. C, figs. 6a-b. 



Shell sub-triangular, length and breadth about equal ; 

 greatest width at the cardinal border, and diminishing rapidly 

 to the front, where it terminates in an obtuse angle ; cardinal 

 border sinuous, terminating exteriorly in small salient ears ; dor- 

 sal valve longitudinally convex, concave from side to side, 

 furnished with two folds, which are very obtuse at the beak, 

 but become rather prominently and broadly angular as they 

 approach the front; sinus indistinct near the beak, large 



