102 BEACHIOPODS. 



and moderately deep in front; tongue of sinus triangular; 

 beak rather obtuse, and rather strongly incurved ; hinge-line 

 sinuous, and situated some distance within the cardinal border ; 

 ventral valve shorter than dorsal valve, convex on the middle, 

 sides nearly perpendicular ; mesial fold indistinct near the beak, 

 becoming broad and somewhat prominent in front. ( Shumard.) 

 Horizon and localities. Lower Carboniferous, Burlington 

 limestone : Columbia ( Boone county ). 



Rhynchonella ringeus SWALLOW. 



Rhynchondla ringeus Swallow, 1860: Trans. St. Louis Acad. Sci., vol. 



I, p. 653. 



Shell very large, heavy, triangular. Surface marked by 12 

 to 14 radiating ridges. 



Horizon and localities Lower Carboniferous, Burling- 

 ton limestone: Fulton (Calla way county), Hannibal (Marion 

 county). 



Rhynchonella subtrigona MEEK & WORTHEN. 



Rhynchonella subtrigona Meek & Worthen, 1860: Proc. Acad. Nat. Sci., 



Phila., p. 451. 



Rhynchonella parvini McChesney, 1861: Desc. New Pal. Foss , p. 83. 

 Camarophora subtrigona Meek & Worthen, 1866: Geol. Sur. Illinois, vol. 



II, p. 251, pi. xvili, figs. 8a-c. 





 A large, robust form like R. cooperensis. 



Horizon and localities Lower Carboniferous, Keokuk 

 limestone : Wayland ( Clark county ). 



Rhynchonella subcuncata HALL. 



Rhynchonella subcuneata Hall, 1856: Trans. Albany Institute, vol. IV, 



p. 11. 

 Rhynchonella subcuneata Hall, 1858 : Geology Iowa, vol. I, p. 658, pi. xxiii. 



figs. 3a-c. 

 Rhynchonella arctirostrata Swallow, 1863: Trans. St. Louis Acad. Sci., 



vol. It, p. 48. 



A rather small, flattened, cuneate shell, with large plica- 

 tions and an obscure mesial sinus. 



Horizon and localities. Lower Carboniferous, Keokuk 

 limestone : Boonville ( Cooper county ). 



