BRACHIOPODS. 79 



Shell quite variable, usually somewhat wider than long, 

 thick ; h^nge-line varying in length from once to twice the 

 length, and often mucronate. Cardinal area narrow. Surface 

 marked by simple rounded ridges, 20 or 25 on each side of the 

 median fold. 



Horhon and localities. Lower Carboniferous, Kinderhook 

 beds: Chouteau Springs ( Cooper county }, Hannibal, Louisi- 

 ana, Clarksville (Pike county), and elsewhere. 



Spirifera peculiaris SHUMARD. 



Spirifer peculiaris Shumard, 1855: Geol. Sur. Missouri, Ann. Rep., p. 202, 

 pi. C, figs. 7a-b. 



A small subglobose form with broad plications. 

 Horizon and localities Lower Carboniferous, Kinderhook 

 limestone : Chouteau Springs ( Cooper county ). 



Spirifera grimesi HALL. 

 Spirifer grimesi Hall, 1858: Geology Iowa, vol. I, p. 604, pi. xiv, figs. 1-5. 



Shell very large, subglobose, usually longer than wide ; 

 hinge-line about three-fourths as long as the greatest width. 

 Dorsal valve less convex than ventral, with a low, broad mesial 

 fold, which becomes quite prominent at the anterior border. 

 Ventral valve very convex, especially toward the umbo ; mesial 

 sinus broad, shallow ; area rather short, moderately high; for- 

 amen wide ; beak incurved. Surface marked by low, broad 

 radiating ribs, which occupy the median fold and sinus as well 

 as the other parts of the shell. The folds again marked by fine 

 longitudinal lines. 



Horizon and localities Lower Carboniferous, Chouteau 

 ( Kinderhook ) limestone : Hannibal, Louisiana, Sedalia; Bur- 

 lington limestone : Palmyra (Marion county), Hannibal, Lou- 

 isiana, Sedalia, Springfield, Ste. Genevieve. 



This species is one of the most characteristic forms of the 

 Burlington limestone. As remarked by Hall, the shell is sel- 

 dom found entire and undistorted, though one of the most 

 abundant and widely distributed forms. The valves are easily 

 separated, and being very thin, the specimens are commonly 

 flattened out, thus making the hinge-line appear much longer 



