292 MISSISSIPPIAN BRACHIOPODA 



15.5 mm., length of hinge-line 13.5 mm., height of cardinal area 3.5 mm. 



Pedicle valve with a prominent umbo, the surface curving rather ab- 

 ruptly anteriorly to the front margin and more gently laterally, slightly 

 or not at all compressed towards the cardinal extremities; mesial sinus 

 sharply defined, originating at the beak, of moderate depth and width, 

 subangular at the bottom ; beak rather sharply pointed, incurved ; cardinal 

 area rather high, nearly flat below and lying in nearly a right angle to the 

 plane of the valve, becoming concave above, the curvature increasing 

 towards the beak, the surface abruptly rounding into the lateral slopes 

 of the valve along the lateral margins; the delthyrium narrowly triangu- 

 lar, higher than wide; each lateral slope bearing from seven to nine 

 simple, rounded or subangular plications which originate near the car- 

 dinal margin and grow successively smaller towards the cardinal ex- 

 tremities, the last two or three usually being very faint. 



Brachial valve depressed convex, much shallower than the pedicle, its 

 greatest convexity near the middle, compressed towards the cardinal 

 extremities ; mesial fold sharply defined, rounded on top, only moderately 

 elevated above the general surface of the valve ; beak small and incon- 

 spicuous, scarcely reaching beyond the cardinal margin; cardinal area 

 very narrow, lying in nearly the plane of the valve ; lateral slopes bearing 

 plications similar to those of the opposite valve and alternate with them. 



Besides the plications, each valve is ornamented by fine, regular, con- 

 centric, sublamellose, imbricating markings, about three or four of which 

 occupy the space of one millimeter. When the shell is perefectly pre- 

 served the surface of each of these concentric lamellae is regularly fim- 

 briate. The shell structure finely and closely punctate. 



Remarks. This species is characterized by its rather high area and 

 the absence of a median plication in the fold and sinus. The fimbriated 

 character of the fine concentric markings of the shell has been observed 

 on but a single example, but it was doubtless characteristic of all during 

 life. The punctate structure of the shell is also usually obscure but can 

 usually be detected upon some specimens of any collection by close ex- 

 amination with a lens. The internal characters of the shell have not 

 been observed, but they doubtless conform with other members of the 

 genus. 



Horizon. Kinderhook. 



SPIRIFERINA SOLIDIROSTRIS White 

 Plate XXXVI, Figs. 25-34 



1860. Spirifer solidirostris White, Jour. Boston Soc. Nat. Hist., vol. 7, 



p. 232. 

 1862. Spiriferina solidirostris White, Proc. Boston Soc. Nat. Hist., vol. 9, 



p. 24. 

 1865. Spiriferina solidirostris Winchell, Proc. Acad. Nat. Sci. Phil., p. 120. 



