PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 463 
D. irregularis. It differs from the latter in its wider hinge, less convex and shorter 
valves. Its small size and similarity to D. gibbosus will serve to identify the 
species in the Mississippi Valley. 
Horizon and locality.—Platteville formation (McGregor member) in Rock 
County, Wis.: At Beloit and Janesville. 
Same formation in Illinois: At Dixon, Lee County. 
DOLEROIDES ? PONDEROSUS Cooper, new species 
Plate 94, C, figures 9-18; plate 94, D, figures 19-21 
Doleroides ? sp. Butts, Virginia Geol. Surv. Bull. 52, pl. 80, figs. 22-24, pl. 81, figs. 34-35, 
1942. 
Subrectangular in outline, with the width greater than the length; lateral mar- 
gins broadly rounded, anterior margin truncated; cardinal extremities obtuse ; 
anterior commissure broadly uniplicate. Surface costellate, costellae narrowly 
rounded, elevated and with interspaces about equal in width to the costellae, 8 
or 9 costellae in 5 mm. at the front margin, some standing out more prominently 
than others. 
Pedicle valve in lateral profile most convex in the posterior half and flattened 
in the front half. Umbonal region convex, the convexity continued forward to 
a point not quite at the middle ; posterolateral slopes long and steep. Sulcus broad 
and shallow, originating at about the middle and occupying slightly more than 
half the width at the anterior margin. Flanks flat in profile with moderately 
gentle slopes to the margins. Interarea short, curved, apsacline. Beak incurved. 
Brachial valve moderately and evenly convex in lateral profile with the maxi- 
mum curvature at about the middle; strongly and broadly convex in anterior 
profile. Umbonal region slightly convex, but anterior to the umbo and through- 
out the median part to the front margin, the shell is fairly strongly swollen and 
produces moderately steep slopes to the margins. Interarea short. 
Pedicle interior with muscle area longer than wide and with narrow diductor 
impressions ; thickened front margin with 2 short ridges anterior to it. 
Measurements in mm.— 
. Brachial Hinge 
Length length Width width Thickness 
TON OLS DE a oe fis iaie'n'« ols, 5,0 apn ialolsig 26.6 24.7 32.6 26.8 15.8 
Paratype’ (110784) i... 25 27.6 25.6 33.8 26.0 ? 
Types.—Holotype: 98225b; figured paratypes: 98225c, 110774, 110778a, 
110784; unfigured paratypes: 98225a, 110778b,c; figured specimens: 118003a,c. 
Horizon and locality —Effna formation in Virginia: At Porterfield Quarry, 
5 miles east of Saltville, Maccrady (T.V.A. 218-NW) Quadrangle; lower part 
McNutt Quarry, 12 miles west of Bland, Burkes Garden (15’) Quadrangle. 
Botetourt formation in Virginia: At the junction of Virginia Highways 731 
and 724, 2 miles northwest of Brownsburg, Lexington (15’) Quadrangle. 
Discussion—This species is unlike any other member of the genus so far 
known in its large size and the alternating nature of the costellae. It was at first 
thought to be referable to Mimella, but the character of the pedicle muscle field 
