410 MISSISSIPPI AN BRACHIOPODA 



siliceous papillae which cover the surface of the specimens, these being 

 the casts of the perforations in the original shell. The species is especi- 

 ally characterized by its small size, the broadly rounded lateral margins 

 of the cardinal area, and the rounded cardinal extremities. 

 Horizon. Keokuk limestone. 



PSEUDOSYRINX GIG AS n. Sp. 



Plate LXVI, Figs. 1-5 



Description. Shell large, broader than long, the greatest width at or 

 near the hinge-line, the cardinal extremities subangular or rounded. The 

 dimensions of a nearly complete specimen are: length of pedicle valve 

 from beak to front 50 mm., length of brachial valve 38 mm., width 82 

 mm., thickness 56 mm., height of cardinal area 43 mm., width of sinus in 

 front 30 mm., width of delthyrium at base 18 mm. 



Pedicle valve subpyramidal in form, the surface sloping with gentle 

 curvature from the umbonal region to the lateral and anterior margins; 

 the mesial sinus non-plicate, of moderate depth, rounded in the bottom 

 and ill-defined laterally, produced anteriorly in a broad, rounded, lingual 

 extension; beak small, pointed, slightly curved over the cardinal area; 

 cardinal area very high, nearly flat from the hinge-line to a point near 

 the apex where it is gently concave for a short distance below the beak, 

 it slopes anteriorly from the hinge-line at an angle of about 40 degrees 

 to the plane of the valve, and its lateral margins round rather 

 abruptly into the lateral slopes of the valve, the triangular, vertically 

 marked differentiated region lying on each side of the delthyrium is 

 large, the base of this larger triangle occupying more than one-half 

 the total length of the hinge-line; delthyrium narrowly triangular, the 

 height more than twice the width; each lateral slope bearing about 16 

 simple, depressed, often ill-defined, radiating plications, which originate 

 along the cardinal margin and become successively smaller towards the 

 cardinal extremities. Internally the hinge-teeth are supported by well- 

 defined dental lamellae which are continued along the floor of the valve 

 for nearly or quite one-half the length of the valve from the beak to the 

 front margin, their divergence anteriorly being about equal to the diverg- 

 ence of the lateral boundaries of the mesial sinus; the delthyrial plate 

 is well developed and extends from the apex of the delthyrium to a point 

 from one-third to one-half the distance to the hinge-line ; it is nearly flat 

 or gently convex transversely and its free margin is a regularly concave 

 curve. 



Brachial valve subsemicircular in outline, with a deep, broadly rounded 

 emargination in front opposite the mesial fold, the greatest convexity is 

 on the median line at the front margin, the surface curves more abruptly 

 to the cardinal margin and is somewhat compressed towards the cardinal 



