BEACHIOPODS. 49 



Froductus nebrascensis Meek, 1872: U. S. Geol. Sur. Nebraska, p. 165, pi. 



ii, fig. 2, ; pi. iv, fig. 6; pi. v. figs, lla-c. 

 Productus nebrascensis White, 1875: U. S. Geog. Sur. w. 100 Merid., vol. 



IV, pt. ii, p. 116, pi. viii, figs. 3a-d. 



Sbell rather below medium size, slightly wider than long; 

 cardinal margin about equal to greatest breadth. Ventral 

 valve moderately arched, most abruptly curved toward the 

 beak, which is incurved and extended beyond the hinge-line ; 

 mesial sinus shallow. Dorsal valve flattened centrally, con- 

 cave toward the margins. Surface marked by broad, concen- 

 tric wrinkles, and obscure, interrupted radiating costse, set 

 with numerous short, stout spines, with fewer long ones inter- 

 spersed. 



Horizon and localities- U pper Carboniferous, Upper Coal 

 Measures : Kansas City. 



This is one of the most abundant and characteristic spe- 

 cies of this genus occurring in the Coal Measures of the Mis- 

 sissippi basin. Although the original figures of Owen are 

 defective and misleading in many particulars, there is now no 

 doubt as to the identity of this species from the various local- 

 ities in the state. 



Korwood & Pratten's P. rogersi described from Huntsville, 

 Missouri, is apparently an internal cast of the shell under con- 

 sideration, in which the radiating ribs and concentric folds are 

 very prominently marked. The forms described by McChes- 

 ney as P. asper&ud. P. wilberanus are manifestly merely local 

 varieties of typical P. nebrascensis, as a careful comparison and 

 examination of a large series of specimens has recently shown. 



As to Geinitz's determinations of this form in the Carbon- 

 formation und Dyas in Nebraska, Meek says substantially as 

 follows : Geinitz was certainly in error in referring this shell 

 to Strophalosia horrescens, since it is positively not a Stropha- 

 losia at all, but a true Productus, as may be seen from any well- 

 preserved specimens. It never has any traces of the cardinal 

 area of the genus Strophalosia, as has been well shown m the 

 careful examination of hundreds of good specimens, its cardi- 

 nal margin being linear. By a comparison with Strophalosia 

 horrescens, as illustrated in Geinitz's work on the German Per- 



