378 MISSISSIPPIAN BRACHIOPODA 



The dimensions of a nearly complete individual are : length 30 mm., 

 width 32 mm., length of hinge-line 20 mm., thickness 21 mm. 



Pedicle valve with its greatest convexity posterior to the middle, the 

 surface curving abruptly from the umbonal region to the cardinal 

 margin, more gently to the anterior and lateral margins, the convexity 

 extending to the cardinal extremities; beak pointed and incurved; car- 

 dinal area about two-thirds the total width of the shell, 5 mm. in height 

 in the type, concave, becoming more curved towards the beak, its inferior 

 portion sloping at an angle of about 115 degrees to the plane of the valve, 

 its lateral margins defined, its surface marked by vertical stria 1 ; delthy- 

 rium rather large, forming a nearly equilateral triangle ; lateral slopes of 

 the valve each bearing about 11 depressed, rounded plications, most of 

 which are simple, although a tendency to divide is occasionally observable, 

 they become progressively smaller towards the cardinal extremities; 

 mesial sinus ill-defined, nearly or quite obsolete at the beak, shallow 

 and rounded in the bottom, occupied by about 7 plications similar in 

 strength to those upon the lateral slopes. 



Brachial valve subelliptical in outline, a little less concave than the 

 pedicle, its greatest convexity near the middle, the surface slightly com- 

 pressed towards the cardinal extremities, the beak projecting a little 

 posteriorly from the hinge-line ; mesial fold scarcely defined at the beak, 

 becoming moderately elevated anteriorly where it is rounded in contour 

 and is not sharply differentiated from the lateral slopes, bearing eight 

 plications, the four central ones being less distinct than the others, in 

 the umbonal region the four central ones have become united into a 

 single median plication and each pair of two lateral ones are also united 

 so there are only three in all, and it is possible that these three also 

 unite into a single one before reaching the beak, but the condition of 

 preservation of the type is not such as to certainly show this; the lateral 

 slopes of the valve bear plications similar in form and number to those 

 of the opposite valve. 



The minute surface markings of the shell are not preserved in the 

 type specimen, but a few rather weak concentric lines of growth are 

 shown. 



Remarks. In general form and appearance this species resembles 8. 

 subcardiiformis and it has usually been so identified. It is easily distin- 

 guished from that species, however, by its much broader cardinal area 

 and by the absence of the false cardinal area which is so conspicuous on 

 that species, as well as by the less sharply defined mesial sinus with its 

 larger number of plications and the occasional tendency of the plications 

 to divide. 



Horizon. Salem limestone. 



