360 MISSISSIPPI AN BRACHIOPODA 



SPIRIPER ROWLEYI n. sp. 

 Plate LIII, Figs. 3-6 ; Plate LIV, Figs. 1-4 



1909. Spirif er grimesi Weller, Bull. Geol. Soc. Am., vol. 20, p. 304, pi. 13, 

 figs. 1-2. ,, 



Description. Shell large, broader than long, transversely subelliptical 

 in outline, the hinge-line shorter than the greatest width, the cardinal ex- 

 tremities subangular or rounded. The dimensions of a nearly complete 

 but somewhat distorted specimen are : length of pedicle valve about 55 

 mm., length of brachial valve about 47 mm., greatest width about 75 mm., 

 length of hinge-line about 55 mm., thickness -f-32 mm. 



Pedicle valve rather strongly convex, the greatest depth posterior to 

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

 the cardinal margin each side of the beak, becoming somewhat compressed 

 towards the cardinal extremities, curving more gently to the lateral and 

 anterior margins; the beak very small and strongly incurved; cardinal 

 area of moderate height, nearly flat towards the cardinal margin but be- 

 coming rather strongly concave towards the beak, the lateral margins 

 sharply defined, subparallel with the cardinal margin for the greater part 

 of their length ; mesial sinus originating as a narrow^ and sharply defined 

 furrow at the beak, becoming broader, less sharply defined and rather 

 deep anteriorly where it is rounded in the bottom and somewhat produced 

 as a rounded anterior extension of the valve; lateral slopes and sinus 

 marked by depressed, rounded, radiating plications which bifurcate fre- 

 quently, they are from one to two millimeters in width, from 25 to 30 

 occupying each lateral slope, and 20 or more the mesial sinus at the front 

 margin. 



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

 pedicle, its greatest depth near the middle, the surface compressed to- 

 wards the cardinal extremities ; the cardinal area very narrow and linear ; 

 the mesial fold well defined to the beak, scarcely elevated above the gen- 

 eral surface in the umbonal region, becoming strongly elevated in front 

 and sometimes slightly recurved, its lateral boundaries less sharply de- 

 fined anteriorly than towards the beak; the entire surface of the valve 

 marked by flattened, bifurcating plications entirely similar in form and 

 number to those of the opposite valve. 



The minute surface markings of the shell are exceedingly fine radiating 

 striae, twenty of which sometimes occupy the width of a single plication. 



Remarks. This species has been identified commonly as 8. grimesi, but 

 it may be easily distinguished from that species by its narrower umbonal 

 region and more pointed beak, and by the narrower, deeper and more 

 sharply defined mesial sinus. The minute radiating striae are also usually 



