BRADLEY: BRACHIOPODA OF THE MAQUOKETA OF IOWA. 507 



Clermont and are the most numerous of the Orthidae in the IVIaquo- 

 keta of that locahty. P. kankakensis is the wider and has more 

 striations. Below is a comparison of average specimens of each. 



Locality: — The Fernvale at ^Yilmington, Illinois and the Lower 

 Maquoketa at Clermont, Iowa. M. C. Z. 8,536. 



Plectorthis (Austixella) whttfieldi (X. H. ^Yinchell). 



Plate 1, fig. 1. 



Orthis whitfieWi N. H. Winchell, 9th Ann. rept. geol. nat. hist. surv. Minnesota, 



1881, p. 115. 

 Orthis yectinella ^Tiitfield (part), Geol. Wise, 1882, 4, p. 259, pi. 12, fig. 8. 

 Plectorthis whitfieldi Hall and Clarke, Pal. N. Y., 1892, 8, pi. 1, p. 221, pi. 5, 



fig. 26. 

 Orthis (Plectorthis) whitfieldi Winchell and Schuchert, Geol. Minn., 1893, 3, 



pt. 1, p. 437, pi. 33, fig. 8-13. 

 Austinella whitfieldi Foerste, Bull. sci. lab. Denison univ., 1909, 14, p. 244 



(gen. ref.); 1912, 17, p. 131, pi. 8, fig. 9. 

 '^Plectorthis sp. cf. whitfieldi Ruedemann, Bull. 162, N. Y. state mus., 1912, 



pi. 4, fig. 8.- 



This species is closely related to Plectorthis (Austinella) karikakemis 

 (YlcChesney) of the Ferm-ale at ^Yilmington, Illinois, but is always less 

 extended along the cardinal area and more square in outline. It is 

 hard to separate these species in some instances, because of the varia- 

 tion in the number of striations which characterizes them both. 

 AMiere they occur abundantly together, as at Clermont, they have a 

 tendency to intergrade into each other. 



The pedicle-valve has a distinct beak; cardinal area arched; del- 

 thyrium triangular. The striations are quite strong; their number 

 varies from thirty-six to forty-eight. This is the chief distinction 

 between whitfieldi and kankakensis, the latter possessing sixty to 

 seventy striae on the anterior margin. The striations in both species 

 increase by implantation. 



The brachial-valve is much less convex than the other; a slight 

 flattening along the middle grades into a slight concavity at the 



