242 MISSISSIPPIAN BRACHIOPODA 



Pedicle valve longitudinally subearinate, with the lateral slopes gently 

 convex, the curvature becoming more abrupt towards the cardinal mar- 

 gins, the margins incurved between the cardinal extremities and the apex 

 of the beak to form a small pseudo-cardinal area lying in nearly the plane 

 of the valve, the valve arched from beak to front along the median line 

 with the curvature somewhat more abrupt posteriorly, the greatest depth 

 of the valve posterior to the middle ; the beak prominent, acutely pointed, 

 very slightly incurved, projecting notably beyond that of the opposite 

 valve ; delthyrium broadly triangular, partially closed by a pair of delti- 

 dial plates which do not meet at the median line, thus leaving a triangular 

 foramen which reaches from the apex to the base. 



Brachial valve less convex than the pedicle, greatest depth posterior to 

 the middle, the surface curving more abruptly to the cardinal margins; 

 beginning just in front of the umbonal region a shallow, sub-angular or 

 rounded mesial sinus, with ill-defined lateral margins, continues with 

 increasing depth to the front margin; lateral slopes of the valve convex 

 transversely from the median line to the lateral margins ; beak obtusely 

 pointed, scarcely or not at all incurved. 



Surface of both valves nearly smooth, marked only by more or less 

 inconspicuous concentric lines of growth which are sometimes nearly 

 obsolete. 



Remarks. This little shell resembles the associated Trigeria curreyi 

 in size and general form, but differs from it in the absence of plications 

 and commonly in the less angular median sinus of the pedicle valve. In 

 its smooth shell it resembles the associated Selenella pediculus, but may 

 be easily distinguished from it by its subearinate pedicle valve, its sinuate 

 brachial valve, and by the more conspicuous concentric lines of growth. 

 The species is referred to the genus Centronella because of its external 

 form alone, the internal characters of neither valve being known, nor 

 has the punctate structure of the shell been detected. 



Horizon. Louisiana limestone of the Kinderhook. 



CENTRONELLA ( ? ) EMACIATA Rowley 

 Plate XXX, Figs. 40-42 



1900. Centronella eniaciata Rowley, Ami. Geol., vol. 25, p. 265, pi. 5, 

 figs. 48-50. 



Description. SShell small, longer than wide, ovate-suibpentagonal in 

 outline, the greatest width posterior to the mid-length; the posterior 

 lateral margins nearly straight and meeting at the beak in an angle of 

 about 80 degrees, posteriorly the margins round rather abruptly into the 

 gently convex antero-lateral margins which in turn pass gradually into 

 the rather short but more convex anterior margin. The dimensions of 

 the holotype are: length of pedicle valve 12.3 mm., length of brachial 

 valve 11.2 mm., greatest width 9.8 mm., thickness 4.1 mm. 



