338 MISSISSIPPIAN BRACHIOPODA 



in the fine, surface markings of the shell, but the less acutely angular, 

 cardinal extremities, and the peculiar contour of the shell, indicated 

 above, afford sufficient means of differentiating the two species. 

 Horizon. Lower Burlington limestone. 



SPIRIFER CRAWFORDSVILLENSIS n. sp. 

 Plate XLVII, Figs. 1-5 



Description. Shell of medium size, much wider than long, the greatest 

 width along the hinge-line, the cardinal extremities acutely angular. The 

 dimensions of a nearly complete example, the holotype of the species, 

 are : length 23 mm., width 47 mm., thickness 13 mm., height of cardinal 

 area 3 mm. 



Pedicle valve only moderately convex in the central portion, becoming 

 compressed towards the cardinal extremities, the umbonal region rather 

 broad, the surface sloping abruptly from it to the cardinal margin for a 

 short distance on each side of the beak, in other directions the slope is 

 gentle ; beak small, acuminate, pointed and incurved ; cardinal area rather 

 narrow, arched, the curvature becoming greater towards the beak, the 

 lateral margins sharply defined, subparallel with the cardinal margin 

 for some distance on each side of the beak, sloping to the cardinal ex- 

 tremities distally, surface of the area marked with vertical strias and by 

 longitudinal lines of growth ; the lateral slopes of the valve each bearing 

 12 to 14 simple, rounded plications which grow successively smaller 

 towards the cardinal extremities; mesial sinus originating at the beak, 

 rounded in the bottom, becoming less well defined anteriorly, marked by 

 plications similar to those on the lateral slopes of the valve except that 

 they are somewhat smaller than those immediately adjacent to the sinus 

 on each side; they consist of a median, simple one which probably orig- 

 inates near the beak, and of one or two lateral ones on each side which 

 originate from the inner margins of the lateral bounding plications. 



Brachial valve about equally convex with the pedicle, its greatest con- 

 vexity near the middle; mesial fold originating at the beak, it is scarcely 

 elevated above the general surface in the umbonal region, but becomes 

 moderately elevated anteriorly where it is rounded in contour, it is 

 marked by about 6 plications which are similar in size and form to those 

 of the sinus of the opposite valve, all of which originate from a single 

 plication at the beak; lateral slopes moderately convex, compressed 

 towards the cardinal extremities, marked by plications which are similar 

 in form and number to those of the opposite valve. 



The minute surface markings consist of fine, crowded, concentric, 

 lamellose lines. At intervals they are more closely crowded and give rise 

 to more conspicuous lines of growth. 



