PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 225 
eldert which it somewhat resembles. The shell of P. biconvexa is unusually 
thick and shows some marks of the internal structure. Unfortunately the speci- 
mens which showed these marks were prepared by burning the shell in a blast 
lamp and then flaking off with a needle. The details obtained are not sufficiently 
clear to make an adequate description of the interior. 
PACHYGLOSSA DORSICONVEXA Cooper, new species 
Plate 11, F, figure 11; plate 28, C, figures 7, 8 
Shell small, brown to blue-gray in color, elliptical in outline with the length 
slightly greater than the width ; greatest width at the middle. Pedicle valve with 
the posterolateral margins nearly straight and forming an apical angle of about 
80° ; sides gently rounded ; anterior margin narrowly rounded ; pedicle valve with 
lateral profile gently convex and with the greatest convexity at about the middle ; 
anterior and posterior slopes gentle ; anterior profile moderately convex. Pedicle 
interior with deep pedicle groove between lateral folds. 
Brachial valve with subequally rounded extremities and gently rounded sides ; 
lateral profile strongly convex; greatest depth about one-third the length from 
the beak; anterior slope long and gentle; anterior profile somewhat narrowly 
rounded and with steep lateral slopes. Beak marginal. Surface of both valves 
marked by irregular, strong concentric undulations. 
Brachial interior with thickened posterior margin which is not inflected. 
Muscle pattern not clear. 
Measurements in mm.—Holotype, length 7.2, width 5.0, thickness 1.8? 
Types.—Holotype: 116758a; figured paratype: 117976; unfigured paratypes : 
116758b-g, 117976a-f. 
Horizon and locality —FPratt Ferry formation in Alabama: 0.2 mile southeast 
of Pratt Ferry, Blocton (15’) Quadrangle. 
Discussion—This species in its strongly convex and elliptical brachial valve 
strongly suggests a small P. biconvexa from the Bromide of Oklahoma. The 
colors are also similar. Nevertheless, the species are different. The Oklahoma 
one is much larger, and the brachial valve is proportionally less convex. 
PACHYGLOSSA ? ELDERI (Whitfield) 
Plate 5, E, figures 12-14 
Lingula elderi WuitrieLp, Amer. Journ. Sci., ser. 3, vol. 19, p. 472, figs. 1, 2, 1880. For 
further synonymy see Bassler, U. S. Nat. Mus. Bull. 92, p. 728, 1915. 
Figured specimens.—24734a, 45015a. 
Horizon and locality.—Platteville limestone (McGregor) and Decorah 
(Spechts Ferry) formation, Minnesota and Wisconsin. 
PACHYGLOSSA PACHYDERMATA Cooper, new species 
Plate 5, F, figures 15-18; plate 6, A, figures 1-5; plate 27, C, figure 8 
Shell of medium to large size, dark brown to black in color, generally thick; 
longer than wide with the length about 14 times the width; valves unequally bi- 
