392 MISSISSIPPIAN BRACHIOPODA 



beak to front margin 28 mm., height of cardinal area 24 mm., greatest 

 width 40 mm., length of hinge-line 36.8 mm., width of sinus in front 14 

 mm., width of delthyrium at hinge-line 10.5 mm. 



Pedicle valve subpyramidal in form, the surface sloping from the umbo 

 to the lateral and anterior margins with a gently convex curvature, the 

 surface of the lateral slopes rounding towards the lateral margins of the 

 cardinal area as they approach the cardinal extremities, but distinctly 

 differentiated from the area ; mesial sinus non-plicate, shallow, rounded 

 iri the bottom, narrow and sharply denned at the beak, becoming broad 

 and less sharply defined anteriorly ; beak erect ; cardinal area flat, sloping 

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

 plane of the valve, the lateral margins sharply denned; delthyrium nar- 

 rowly triangular, its height twice or more than twice its width at the 

 base ; each lateral slope marked by 14 or more simple, depressed, radiat- 

 ing plications which originate near the cardinal margin and become faint 

 or nearly obsolete towards the cardinal extremities where the surface 

 curves towards the cardinal area. Internally the dental lamellae are 

 rather short and somewhat thickened, their divergence being a little 

 greater than that of the sides of the mesial sinus ; the muscular scars are 

 rather strongly impressed in the older specimens, and are short, subovate 

 in outline, with a distinct, median, longitudinal ridge ; the delthyrial 

 plate extends less than half way from the apex of the delthyrium to the 

 hinge-line, it is convex transversely on its outer surface or is marked by a 

 rather broad, rounded, median, longitudinal elevation whose sides slope 

 to the lateral margins of the plates, the free extension of the syrinx is 

 apparently short. 



The minute surface markings of the shell are not capable of preserva- 

 tion in the medium in which the specimens occur, but a few inconspicuous, 

 concentric lines of growth are present upon most of the specimens. 



Remarks. This species is established upon several specimens of pedicle 

 valves preserved as internal casts and external moulds in a friable sand- 

 stone. It resembles S. extenuatus in some respects, but has a greater angle 

 between the cardinal area and the plane of the valve, a relatively higher 

 area, and the cardinal extremities are nearly rectangular or rounded in- 

 stead of extending into acutely angular points. It differs from S. platy- 

 pleurus in its somewhat lower cardinal area and the rounded or quadrangular 

 cardinal extremities, and in the broad, transverse convexity of the del- 

 thyrial plate instead of the subquadrangular, elevated, longitudinal, 

 median rib. It is not at all similar to any of the other species w r ith 

 flat cardinal area and can be distinguished from others by the proportions 

 and flatness of the cardinal area. 



Horizon. Bushberg sandstone of the Kinderhook. 



