460 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
gently swollen and with short and steep lateral and posterolateral slopes. Muscle 
scar narrowly rounded. 
Brachial valve moderately convex in lateral profile, strongly convex and with 
short, steep slopes in anterior profile; sulcus shallow and narrow, originating at 
the umbo but indistinctly visible anterior to the middle; median and lateral areas 
strongly swollen. Notothyrial cavity narrow, supporting plates somewhat erect, 
median ridge wide, stout. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
FAGIGEV PO he cara cclegis ccmeie eee 14.0 12.7 15.9 10.8 0.4 
Paratype 9(110748).| shire sg «ape. 12.7 12.0 15.4 10.9 0.2 
5a (TTIOSIOD) yas 2's 12.4 11.8 14.5 Li2 9.1 
Types.—Holotype: 110648a; figured paratypes: 110510a, 118006a; unfigured 
paratypes: 110510b, 110648, 110748, 118006b. 
Horizon and locality—Dryden formation in Tennessee: 1 mile west of Lone 
Mountain; Tazewell road, 14 miles northeast of Lone Mountain, Tazewell 
(T.V.A. 154-NE) Quadrangle. Evans Ferry section along U. S. Highway 25E, 
north of Indian Creek; 14 miles northeast of Halls School, Howard Quarter 
(T.V.A. 162-NW) Quadrangle. 
Discussion—This is a small, compact species occurring in the Wardell-Ben- 
bolt=Dryden formation of the belts near the Cumberland Front. It has the 
appearance of a small example of D. gibbosus but differs importantly from that 
species. In general the sulcus of the Tennessee species is shorter than that of the 
Minnesota form, and the brachial valve is deeper. This makes the Tennessee 
species somewhat thicker than the Minnesota one. This species differs from 
D. regularis in its narrower hinge and greater thickness as well as in its less 
uniform character. 
DOLEROIDES MISSOURIENSIS Cooper, new species 
Plate 94, B, figures 4-8 
Shell fairly large, resembling D. tennesseensis; wider than long with a mod- 
erately wide hinge; sides rounded; anterior margin gently rounded; anterior 
commissure with a broad uniplicate wave; costellae unequal in size, the larger 
ones concentrated in the median region ; costellae about 10 to 12 in 5 mm. at the 
front margin. 
Pedicle valve unevenly convex, the posterior half moderately convex, the an- 
terior half flattened. Anterior profile broadly but gently convex; posteromedian 
region and umbo swollen; sulcus originating slightly posterior to the middle, 
narrow, shallow, producing a small anterior tongue; flanks somewhat inflated 
but with steep posterolateral slopes. Interarea long, apsacline ; muscle field large, 
somewhat oval in outline; adductor track narrow; dental plates prominent. 
Brachial valve moderately convex in lateral profile; strongly convex in an- 
terior profile; sulcus originating on umbo, shallow, narrow, extending to a point 
anterior to the middle ; anteromedian region somewhat swollen but without forma- 
