352 MISSISSIPPIAN BRACHIOPODA 



ill-defined and plicated, a median plication originates near the beak and 

 continues without division to the anterior margin, on each side there 

 are 4 or 5 plications which originate from the inner margins of the bound- 

 ing plications or through the bifurcation of such plications. 



Brachial valve about as convex as the pedicle, the greatest convexity 

 near the middle, the surface becoming compressed towards the cardinal 

 extremities; mesial fold defined to the beak, slightly elevated above the 

 general surface of the valve in the umbonal region, becoming rather highly 

 elevated in front, rounded or subangular along the median line, marked 

 by plications similar to those of the sinus of the pedicle valve ; lateral 

 slopes most convex towards the umbonal region, marked by plications 

 entirely similar in form and number to those of the opposite valve. 



Remarks. This species resembles 8. keokuk in some respects, but besides 

 usually growing to a larger size, its plications are more numerous on 

 both the lateral slopes and the fold and sinus, they bifurcate more fre- 

 quently and are not so strongly elevated as in that species. The minute 

 surface markings of the shell are not sufficiently well preserved on either 

 of the specimens examined to determine all their characters, but so far 

 as they are preserved they are not unlike those of S. keokuk. 



Horizon. Knobstone formation of Indiana. 



SPIEIFER INDIANENSIS n. sp. 



Plate L, Figs. 6-12 



Description. Shell below medium size, longer than wide, the greatest 

 width a little in front of the cardinal line, the cardinal extremities ob 

 tusely angular or rounded. The dimensions of a nearly complete example 

 are: length 28.5 mm., width 22.5 mm., thickness 19 mm.; the dimensions 

 of a perfect pedicle valve are: length 28 mm., width 25 mm., length of 

 hinge-line 20 mm., convexity 12 mm. 



Pedicle valve with its greatest convexity near or a little posterior to the 

 middle, the surface curving abruptly from the umbonal region to the 

 cardinal margin, more gently to the antero-lateral margins, the convexity 

 of the valve extending out to the cardinal extremities ; beak pointed and 

 strongly incurved ; cardinal area concave, becoming more curved towards 

 the beak, its height 4 to 5 mm., its inferior portion sloping posteriorly at 

 an angle of 140 degrees or more to the plane of the valve, the lateral mar- 

 gins defined, sloping from the beak to the cardinal extremities with a 

 gently convex curve, the surface marked by vertical stria? ; lateral slopes 

 of the valve each bearing 9 or 10 simple, low, rounded plications which 

 grow gradually smaller towards the cardinal extremities ; the mesial sinus 

 originates at the beak where it is shallow and rounded in the bottom, it 

 becomes relatively shallower in the anterior half of the shell where it 

 is often rather ill-defined, its anterior margin is produced into a nasute 



