124 MISSISSIPPIAN BRACHIOPODA 



group of rather delicate spines which originate from the cardinal 

 auriculations of the pedicle valve and attain an extreme length of about 

 30 mm. The specimen described by Hall as P. setigerus var. keokuk is 

 a good example of P. viminalis White, from which P. setigerus differs 

 in its smaller size, its finer costas, its proportionally more elongate hinge- 

 line, and the larger cardinal auriculations. In some respects, especially in 

 its relatively fine costae, P. setigerus suggests P. altonensis of the Salem 

 limestone, but it is larger than that species with relatively larger car- 

 dinal auriculations and possesses a slight median sinus in the pedicle 

 valve. 



Horizon. Keokuk limestone. 



PRODUCTUS ALTONENSIS Norwood and Pratten 

 Plate X, Figs. 14-24 



1855. Productus altonensis Norwood and Pratten, Jour. Phil. Acad. Sci. 



(2), vol. 3, p. 7, pi. 1, figs. la-c. 



1894. Productus altanensis Keyes, Mo. Geol. Surv., vol. 5, p. 43. 

 1906. Productus burlingtcnensis Beede, 30th Ann. Rep. Geol. Surv. Ind., 



p. 1301, pi. 17A, figs. 1-lc. 

 1906. Productus gallatinensis Beede, 30th Ann. Rep. Geol. Surv. Ind., p. 



1302, pi. 17A, figs. 2-2a. 



Description. Shell a little below medium size, usually a little wider than 

 long, the greatest width about the mid-length of the shell, the hinge-line 

 nearly or quite equaling the greatest width. The dimensions of a pedicle 

 valve are: length from hinge-line to front margin 18 mm., length from 

 umbonal region to front margin 22.5 mm., width 24.2 mm., length of 

 hinge-line 24 mm., convexity 16 mm. 



Pedicle valve gibbous, the umbonal region conspicuously protuberant 

 beyond the hinge-line, its sides converging rather rapidly towards the 

 beak, the angle of convergence often being less than 90 degrees, the 

 surface dropping abruptly to the cardinal margin, nearly regularly 

 arched from the umbonal region to the front margin, curving abruptly to 

 the lateral margins, compressed towards the cardinal extremities in flat- 

 tened auriculations of moderate size ; mesial portion of the valve broadly 

 flattened with the flattened region illdefined laterally, mesial sinus com- 

 monly obsolete, when present it is very slight ; beak pointed and strongly 

 incurved. Surface of the valve marked by rather fine radiating plica- 

 tions which are subangular posteriorly, becoming more rounded an- 

 teriorly, from three to four usually occupy the space of 2 mm. in front, 

 in the posterior portion of the valve the costse increase frequently by 

 bifurcation, but anteriorly they continue with few or no divisions to the 

 front margin; upon the lateral slopes of the valve, adjacent to and 

 upon the auriculations, conspicuous, wrinkle-like, concentric markings 



