114 MISSISSIPPIAN BRACHIOPODA 



PRODUCTUS MESICOSTALIS n. sp. 

 Plate XI, Figs. 12-16 



Description. Shell of medium size or smaller, broader than long, the 

 hinge-line apparently a little shorter than the greatest width. The di- 

 mensions of a somewhat incomplete pedicle valve are : length from hinge- 

 line to anterior margin 16.2 mm., length from umbonal region to anterior 

 margin 17.5 mm., length of hinge-line approximately 18 mm., greatest 

 width of shell 22 mm., convexity of pedicle valve approximately 13 mm. 



Pedicle valve strongly convex, the umbonal region only moderately 

 produced beyond the hinge-line, the beak incurved, the surface curving 

 more abruptly to the cardinal margin, the curvature to the lateral and 

 anterior margins about equal, the cardinal auriculations small; mesial 

 sinus originating in the umbonal region, shallow, rather narrow, and ill- 

 defined laterally. Surface of the valve marked by rounded, radiating 

 plications, increasing by bifurcation, and somewhat irregular in size; 

 along the median line is one plication which is notably larger than any 

 of the others and which is bordered on either side by a broader and 

 deeper furrow ; on the posterior surface of the valve the radiating mark- 

 ings are crossed by concentric plications which are fainter in the median 

 portion, becoming wrinkle-like towards the cardinal auriculations; spine 

 bases not distinctly shown. 



Brachial valve gently concave posteriorly, becoming more abruptly 

 curved anteriorly and antero-laterally, being produced nearly in contact 

 with the anterior and antero-lateral portions of the opposite valve ; ante- 

 riorly the mesial portion of the valve is raised in a low mesial fold to cor- 

 respond with the sinus of the opposite valve. Surface of the valve marked 

 by radiating plications similar to those of the opposite valve. 



Remarks. All examples of this species which have come under ob- 

 servation are more or less incomplete, so that many details of the shell are 

 not yet satisfactorily determined, but the species is especially character- 

 ized by the conspicuous mesial plication in the shallow sinus of the ped- 

 icle valve, and no difficulty has been found in the identification of any 

 specimen. 



Horizon. English River Grit-stone of the Kinderhook. 



PRODUCTUS VIMINALIS White 

 Plate XI, Figs. 6-11 



1858. Productus setigerusf var. keokuk Hall, Geol. Iowa, vol. 1, pt. 2, 



p. 639, pi. 19, figs. 4b-c. 

 1862. Productus viminalis White, Proc. Boston Soc. Nat. Hist., vol. 9, 



p. 29. 

 1883. Productus semireticulatus Hall, Rep. N. Y. State Geol. for 1882, 



pi. (18), 49, fig. 12 (not 11 and 13). 



