PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 467 
ately convex but the anterior half somewhat flattened. Anterior profile almost 
flat to broadly and gently convex ; umbonal region swollen, sulcus originating at 
about the middle, broad and shallow at its origin but widening and deepening to 
the anterior margin where it occupies nearly half the width; flanks bounding 
sulcus gently convex ; posterolateral extremities narrowly convex and with steep 
slopes, and strongly deflected toward the brachial valve. Interarea long, curved, 
apsacline. Muscle field long with subparallel sides ; adductor track wide at front ; 
diductor scars long and narrow. 
Brachial valve deeper than the pedicle valve, gently convex in lateral profile, 
strongly convex in anterior profile. Fold originating at about middle, low and 
wide and only moderately elevated ; flanks gently convex ; posterolateral extremi- 
ties gently sulcate ; lateral slopes steep. 
Measurements in mm.—Hypotype (110578a), length 17.0, brachial length 
15.3, width 20.8, hinge width 15.8, thickness 10.0. 
Types.—Figured hypotypes: 110578a,b. 
Horizon and locality.—Decorah formation (Spechts Ferry member) in Min- 
nesota: At Fountain, Fillmore County. 
Same formation in Wisconsin: At Highland, Iowa County; 2 miles west of 
Platteville, Grant County. 
Discussion.—This species is characterized by its large size, wide hinge, promi- 
nent and somewhat elevated fold, and strongly uniplicate anterior commissure. 
It differs from D. gibbosus with which it has been confused in the character of 
the brachial fold and the abbreviation of the brachial sulcus. In D. winchelli the 
sulcus on the brachial valve is narrow and shallow and extends anteriorly to 
about the middle. It is also independent of the fold on which it occurs. In 
D. gibbosus, on the other hand, the fold is rather a broad but strong wave of the 
anterior commissure, but the sulcus originates at the beak, is shallow, extends 
anteriorly, widening in the same direction to the anterior margin, where, how- 
ever, it does not affect the commissure. The pedicle sulcus is also more pro- 
nounced in D. winchelli than in D. gibbosus. The name Orthis media was pre- 
occupied, therefore the name D. winchelli is proposed. 
DOLEROIDES sp. 1 
Plate 95, D, figures 29, 30 
Shell large for the genus, subrectangular in outline, wider than long; costellae 
fairly even, 10 to 11 in the space of 5 mm. at the anterior margin; costellae with 
fine scattered pits on surface. 
Pedicle valve with swollen umbo and median region; sulcus occupying anterior 
third, shallow but wide; flanks gently convex ; interarea long, apsacline. Muscle 
field small, narrowly elliptical in outline. 
Brachial valve moderately convex in lateral profile; strongly convex in an- 
terior profile; sulcus scarcely defined, not reaching the margin; median and 
lateral regions swollen ; lateral slopes short and steep. 
Measurements in mm.—Pedicle valve, length 14.7, width 18.9. 
