326 MISSISSIPPIAN BRACHIOPODA 



Remarks. This species may be easily recognized by its high cardinal 

 area, its extended hinge-line, and especially by its broad, flattened fold 

 and sinus whose plications are essentially parallel with the median line 

 of the shell. 



Horizon. Lower Burlington limestone. 



SPIRIFER LEGRANDENSIS n. sp. 

 Plate XL, Figs. 24-29 



Description. Shell below medium size, broadly subtriangular in out- 

 line, the width more than twice the length, the greatest width along the 

 hinge-line, the cardinal extremities acutely angular. The dimensions of 

 a nearly perfect individual are: length of pedicle valve from beak to 

 front 17.5 mm., length of brachial valve 14.5 mm., width along hinge-line 

 36 mm., thickness 15.5 mm., height of cardinal area 7 mm. 



Pedicle valve broadly subpyramidal in form, the greatest depth nearly 

 opposite the hinge-line ; beak small, sharply pointed, moderately incurved 

 over the area; cardinal area high, broadly subtriangular in outline, the 

 inferior portion nearly flat and making an angle of about 90 degrees to 

 the plane of the valve, becoming concave towards the beak, lateral mar- 

 gins sharply defined, sloping regularly from the beak nearly to the car- 

 dinal extremities beyond which point the slope becomes more abrupt, del- 

 thyrium higher than wide ; lateral slopes gently convex, the curvature 

 most abrupt to the cardinal margin near the beak, each marked by from 

 16 to 18 simple, subangular plications which become successively smaller 

 towards the cardinal extremities; mesial sinus shallow, sharply defined 

 from beak to front by angular plications, marked by a median plication 

 which originates near the beak and becomes strong and angular towards 

 the front, in the larger individuals each side of the sinus is marked by a 

 single plication much weaker than the median one, which originates from 

 the inner margins of the lateral bounding plications. 



Brachial valve much shallower than the pedicle, with a narrow, linear 

 cardinal area; mesial fold low, flattened on top, sharply defined to the 

 beak where it is simple, in the umbonal region the single plication is 

 divided into two by a median furrow corresponding to the median plica- 

 tion of the opposite valve, each side being again divided in the larger ex- 

 amples between the umbo and the front of the shell ; lateral slopes convex 

 antero-posteriorly, the surface curving much more abruptly to the cardinal 

 margin, each marked by plications similar in form and number to those of 

 the opposite valve. 



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

 specimens observed, but several concentric lines of growth are present 

 which are more crowded towards the front of the shell. 



Remarks. This species has sometimes been identified as 8. biplicatus, 



