64 MISSISSIPPIAN BRACHIOPODA 



of the pedicle .valve, the concavity being distributed through the entire 

 length of the valve, and in the abruptly elevated umbonal region ; the two 

 species are similar in their narrow cardinal areas, the two lateral margins 

 of which form nearly a straight line. 

 Horizon. Kinderhook. 



SCHELLWIENELLA CHOUTEAUENSIS n. Sp. 



Plate VII, Figs. 5-8 



Description. Shell of medium size or a little larger, broader than long, 

 the hinge-line nearly or quite equaling the greatest width, the cardinal 

 extremities angular, the lateral margins nearly straight or gently convex 

 posteriorly, becoming more convex anteriorly and rounding without in- 

 terruption into the convex anterior margin. The dimensions of a nearly 

 complete specimen are : length of pedicle valve 23 mm., length of brachial 

 valve 21 mm., greatest width 27.5 mm., length of hinge-line 24.5 mm., 

 convexity of brachial valve 4.8 mm., height of cardinal area 3.8 mm. 



Pedicle valve concave or sometimes nearly flat, most prominent on the 

 umbo which is raised above the remaining surface of the valve ; mesial 

 sinus obsolete; beak obtusely angular, erect; cardinal area of moderate 

 width, flat, with sharply angular lateral margins which slope from the 

 beak to the cardinal extremities in nearly straight lines; the delthyrium 

 wider than high, closed by a convex deltidium with a concave cardinal 

 margin. Internal characters not observed. 



Brachial valve moderately convex, the greatest convexity posterior to 

 the middle, the surface curving gently from the highest point to the lateral 

 and anterior margins, a little more abruptly to the cardinal margin, 

 somewhat compressed towards the cardinal extremities; mesial fold 

 obsolete ; beak inconspicuous, not extended beyond the cardinal margin ; 

 cardinal area very narrow, making an obtuse angle with that of the 

 opposite valve, the middle of the hinge-line marked by the rather prom- 

 inent posterior extremity of the cardinal process which fills the concave 

 cardinal excavation of the deltidium of the opposite valve. Internal 

 characters not observed. 



Surface of both valves marked by rather coarse radiating costae which 

 are similar on the two valves, about two occupying the space of one 

 millimeter. The costas are crossed by regular, strong, irregularly distrib- 

 uted, concentric lines of growth which are commonly more crowded to- 

 wards the front of the shell. 



Remarks. This species from the Chouteau limestone is perhaps more 

 closely similar to 8. inaqualis than to any other species of the genus here 

 considered, but it is a more coarsely costate shell than that one. 



Horizon. Chouteau limestone. 



