668 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
angle 80°. Anterior commissure sulcate. Pedicle valve deeper than the brachial 
one. Costate; costae numbering Io or II. 
Pedicle valve evenly and moderately convex in lateral profile, broadly convex 
in anterior profile and with the highest point at the middle to form a subcarinate 
profile. Umbo not swollen; median costa more elevated than the others and form- 
ing a ridge from umbo to front margin; costa on each side of umbo slightly ele- 
vated so that the 3 costae form a fold. Flanks flattened and with steep slopes. 
Brachial valve gently convex in lateral profile and concave in anterior profile. 
Sulcus originating on the umbo and extending to the anterior margin; sulcus 
occupied by 2 costae which rise anteriorly to form an indistinct fold within the 
sulcus. Flanks moderately swollen. 
Measurements in mm.—Holotype, length 2.7, brachial length 2.4, width 2.0, 
thickness 1.1. 
Types—Holotype: 117192; figured paratypes: 117193a-c; unfigured para- 
types: 117193d-f. 
Horizon and locality—Lenoir formation in Tennessee: On the south side of 
the cemetery at Friends Church, north corner of Friendsville, Concord (T.V.A. 
138-SW) Quadrangle; Indian Creek, 14 miles south of Bluff City, Bluff City 
(T.V.A. 198-NE) Quadrangle. 
Discussion.—This species is characterized by its small size and few costae. It 
is most like Dorytreta bella but is smaller and less numerously costate. 
The holotype is not a fully grown specimen because it has not attained maxi- 
mum thickness or length. All the other specimens besides the figured ones are 
imperfect. The longest one is about 3.1 mm. in length, and the maximum thick- 
ness observed is 1.7 mm. 
DORYTRETA ? REVERSA Cooper, new species 
Plate 124, J, figures 55-61 
Shell small, elongate oval in outline, biconvex but with the pedicle valve 
slightly deeper than the brachial valve; sides gently rounded; anterior margin 
subnasute; anterior commissure intraplicate; surface marked by Io angular 
costae, 2 in the sulcus, 3 on the fold, and 3 or 4 on the flanks. 
Pedicle valve moderately convex and with the posterior and anterior regions 
more rounded than the median area. Anterior profile broadly convex. Umbonal 
region somewhat flattened. Fold originating about 2 mm. anterior to the beak, 
consisting of 3 costae, the outer 2 strongly elevated but the median one depressed 
in a deep and narrow sulcus in the fold. Flanks flattened and depressed below 
the fold and with steep lateral slopes. Beak moderately incurved ; foramen small. 
Brachial valve moderately convex in lateral profile but with a distinct bulge be- 
tween the umbo and the middle. Gently but broadly convex in anterior profile. 
Sulcus originating at the umbo, shallow and narrow but widening and deepen- 
ing anteriorly to occupy about three-fourths the width at the front margin. Sul- 
cus with 2 costae appearing I mm. anterior to the beak, these costae strengthen- 
