56 MISSISSIPPIAN BBACHIOPODA 



tremities and gently convex from the beak towards the lateral and an- 

 terior margins, the umbo not protuberant beyond the cardinal margin; 

 the mesial portion of the valve usually somewhat flattened from the 

 beak to the front margin, sometimes slightly depressed to form a very 

 shallow, ill-defined sinus; the cardinal area very narrow with sharply 

 defined lateral margins, forming an obtuse angle with that of the opposite 

 valve. Internally the cardinal process is short and rather thick, bifid 

 posteriorly, with a chilidium adjacent to the cardinal margin which 

 occupies the concavity in the base of the deltidium of the opposite 

 valve ; from either side of the cardinal process the socket plates or ridges 

 diverge and are then recurved to the cardinal margin to form the sockets ; 

 the muscular scars subovate in outline, reaching beyond the middle of 

 the valve and more deeply impressed than those of the opposite valve, 

 sometimes divided longitudinally by a rather broad, slightly raised 

 median ridge which continues to the base of the cardinal process. 



Surface of both valves marked by sharp, narrow, radiating costae which 

 increase by bifurcation and intercalation, about three occupy the space 

 of one millimeter at the front of mature shells. The costae are crossed 

 by fine concentric markings, when the surface is well preserved, 

 which give them a crenulated appearance, and by much stronger con- 

 centric lines of growth which are not infrequently crowded towards the 

 front of the shell. 



Remarks. This species has been selected by Girty 1 as the type of his 

 genus Schuckertella. It is a very characteristic member of the Louisiana 

 limestone fauna, and never attains a large size, the largest individual 

 observed by the writer having a length of 16 mm. 



Horizon. Louisiana limestone. 



SCHUCHERTELLA RUBRA Weller 



Plate III, Figs. 10-11 



1909. Orthothetes rubra Weller, Bull. Geol. Soc. Am., vol. 20, p. 294, 

 pi. 12, fig. 5 (not fig. 4). 



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

 than long, the greatest width near the mid-length, the hinge-line straight, 

 a little shorter than the greatest width, the cardinal extremities angular, 

 the central portion of the anterior margin nearly straight or slightly 

 emarginate. The dimensions of a somewhat crushed specimen preserving 

 both valves are: length of pedicle valve 25.3 mm., length of brachial 

 valve 24 mm., greatest width 36 mm., length of hinge-line 32 mm., thick- 

 ness approximately 10 mm., height of cardinal area approximately 3 mm. 



Pedicle valve gently convex, greatest convexity posterior to the middle, 



IProc. U. S. Nat. Mus., vol. 27, p. 734 (1904). 



