314 MISSISSIPPIAN BRACHIOPODA 



Brachial valve depressed convex, usually much less convex than the 

 pedicle valve, the greatest convexity near or posterior to the middle, the 

 surface somewhat compressed towards the cardinal extremities; mesial 

 fold depressed, usually not elevated above the general surface of the 

 valve posteriorly and but slightly elevated anteriorly, bounded by a pair 

 of furrows somewhat deeper and stronger than those between the plica- 

 tions, marked by plications similar in form and number to those of the 

 sinus of the opposite valve, all of which originate through the division of 

 a single one at the beak ; lateral slopes convex towards the middle of the 

 valve, the curvature more abrupt towards the cardinal margin, com- 

 pressed towards the cardinal extremities, marked by plications similar 

 in form and number to those of the opposite valve. 



Surface of both valves marked by fine, concentric, subimbricating lines 

 which are crowded at intervals to form lines of growth of greater or 

 less strength. 



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

 but it is quite different from that species, being more closely allied to 

 8. vernonensis. It differs from S. vernonensis, however, in being marked 

 by more numerous and finer plications, those upon the fold and sinus 

 being equally prominent with those upon the lateral slopes, in not having 

 the sinus of the pedicle valve produced anteriorly and consequently 

 lacking the strongly elevated fold of the brachial valve. It differs from 

 8. osagensis in its larger size, its more numerous and sometimes bifurcating 

 plications upon the lateral slopes, and in the larger number of plications 

 upon the fold and sinus. The species is in some respects intermediate in 

 character between 8. vernonensis and 8. csagensis. 



Horizon. Pierson limestone of the Kinderhook. 



SPIRIFER OSAGENSIS Swallow 

 Plate XXXVII, Figs. 18-21 



1860. Spirifer osagensis Swallow, Trans. St. Louis Acad. Sci., vol. 1, p. 641. 

 1899. Spirifer marionensis Weller, Trans. St. Louis Acad. Sci., vol. 9, 

 p. 17, pi. 4, fig. 12. 



Description. Shell of medium size or smaller, subsemi circular or sub- 

 semielliptical in outline, the greatest width along the hinge-line, the 

 cardinal extremities mucronate. The dimensions of two rather small but 

 nearly complete individuals with the mucronate cardinal extremities de- 

 stroyed are: length of pedicle valve 16.5 mm. and 15.5 mm., length of 

 brachial valve 15.3 mm. and 14.8 mm., width, exclusive of cardinal ex- 

 tremities, 22 mm. and 19.5 mm., thickness 13 mm. and 12.5 mm., height 

 of cardinal area 2.5 mm. and 2.3 mm. 



Pedicle valve rather strongly convex, the greatest convexity posterior 

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



