PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 465 
Dryden formation in Tennessee: Road along Little Sycamore Creek 4 mile 
northeast of the west edge of Howard Quarter (T.V.A. 162-NW) Quadrangle. 
Discussion.—This species is characterized by medium size, fairly regular form, 
moderately strong costellae, rectimarginate anterior commissure, and moderately 
wide hinge. It differs from D. irregularis in its wider hinge and less convex 
valves. It suggests D. extensus but is not so strongly costellate and not so wide. 
This species differs from D. tennesseensis in having more nearly equally deep 
valves and a more regular outline. 
DOLEROIDES TENNESSEENSIS Cooper, new species 
Plate 93, C, figures 15-30; plate 94, A, figures 1-3 
Shell of about medium size for the genus, wider than long, with the greatest 
width anterior to the middle. Hinge narrow; cardinal extremities obtusely angu- 
lar; sides slightly rounded in the posterior half but narrowly rounded at the 
anterolateral extremities. Anterior commissure broadly uniplicate: Costellae of 
unequal size, some swollen and hollow, appearing in 4 generations by intercala- 
tion. The strongest costellae occupy the fold and sulcus where 2 narrow costellae 
may appear between the larger ones and extend for a considerable distance with- 
out expanding or swelling into normal size. From Io to 12 costellae occupy a 
space of 5 mm. at the front margin of the fold and sulcus, while 14 to 16 costellae 
of various sizes may be counted in 5 mm. on the flanks. All costellae perforated 
by small scattered pits. 
Pedicle valve moderately convex in lateral profile with the maximum con- 
vexity in the posterior half; anterior profile broadly and gently convex. Sulcus 
broad and shallow, usually originating near the middle and occupying from 
slightly less than one-half to one-third the width. Umbonal region convex, in 
some specimens distinguished as a low fold that may extend to about the middle 
and in some specimens may be continued anteriorly as a low rounding of the 
shell surface in the sulcus. Flanks gently convex with gentle lateral slopes but 
with steeper posterolateral slopes to the cardinal extremities which are deflected 
slightly toward the brachial valve. Interarea moderately long, curved, apsacline. 
Beak pointed and incurved. 
Brachial valve moderately and evenly convex in lateral profile with the great- 
est convexity at about the middle; anterior profile moderately and somewhat 
narrowly convex with the top of the curve flattened and the sides flat but de- 
scending with fairly steep slopes. Umbonal region marked by a narrow and shal- 
low sulcus which may extend to the front margin or disappear near the middle. 
Sulcus impressed in a broad and poorly defined fold that is most pronounced in 
the anterior half of the valve and is best seen on the anterior commissure. Flanks 
flattened and with moderately steep slopes to the margins. Interarea short, 
apsacline. 
Interior: Pedicle muscle field elongate-oval in outline, not greatly widened 
anteriorly with long and slender diductor impressions and a slightly elevated 
adductor field. Adjustor impressions narrow. Dental plates short with shallow 
umbonal cavities. Pallial impressions not preserved. 
