PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 375 
Pedicle valve moderately strongly convex in lateral profile with the greatest 
convexity in the posterior half; lateral profile strongly and broadly convex; 
umbonal and lateral regions swollen; sulcus originating about 12 mm. anterior to 
the beak, narrow and shallow and forming a short tongue; slopes to cardinal 
extremities very steep. Median costella extending for 3 mm. anterior to the 
beak where it trifurcates, the resulting 3 costellae extending to the anterior mar- 
gin. Interarea curved, gently apsacline. 
Brachial valve strongly convex in lateral profile with the greatest convexity 
at about the middle; anterior profile strongly arched and swollen; median re- 
gion strongly swollen with steep slopes to all margins ; umbo sulcate, sulcus nar- 
row and deep, extending to about the middle where its surface is elevated into 
a low fold; sulcus occupied by 2 costellae at posterior; 2 costellae intercalated 
inside the posterior 2 at 3 mm.; 2 additional costellae intercalated at about 6 
mm, to form a median fascicle of 6 costellae which form the fold. Interarea long 
and strong, curved to overhang the delthyrium. 
Pedicle interior characterized by a deep and broad delthyrial cavity; muscle 
field wide with diductor ends extended anterior to the delthyrial cavity ; adductor 
track short, elevated; median ridge thick. Teeth stout, fossettes deep. Dental 
plates long and thick, umbonal cavities nearly filled. 
Brachial valve with short, stout brachiophores supported by thick swelling of 
the notothyrial platform ; cardinal process bulbous in the adult. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
HAGIOEY PE) inact ieisicise eps s saclay eis sieges 17.9 16.7 20.4 12.2 II.9 
Paratype (pedicle valve 116940b).. 16.2 ? 17.6 12.6 5.5 
" (brachial valve 116940a). ? 17.9 20.0 13.2 7.0 
Types.—Holotype: 84015; figured paratypes: 116940a,b. 
Horizon and locality—Decorah formation (Ion member) in Iowa: At 
Decorah. 
Same horizon in Minnesota: In a road cut 1.1 miles east of U. S. Highway 
52, on the south edge of Cannon Falls; and at Kenyon, Goodhue County. 
Discussion.—The rounded outlines and strongly convex valves set this species 
apart from any of the Appalachian species except G. equiconvexa. The latter is 
very easily separated from G. subcircularis by its subquadrate form and heavy 
shells. Glyptorthis subcircularis is similar to G. bellarugosa and is probably re- 
lated to it. The stronger costellae, the subcircular form, the outline, and strong 
convexity serve to distinguish the two species. 
GLYPTORTHIS SULCATA Cooper, new species 
Plate 46, E, figures 24-34 
Hebertella bellarugosa RAyMonD, Ann. Carnegie Mus., vol. 7, No. 2, p. 245, pl. 36, figs. 8, 9, 
IQII. 
Shell small for the genus, with the length and width about equal. Hinge equal 
in width to the width of the shell or a little less than the greatest width. Cardi- 
nal extremities slightly obtuse. Lateral margins straight to well rounded ; front 
