280 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
deeply concave just anterior to the beak but the concavity flattening anteriorly. 
Greatest convexity of posterior slope located in vicinity of pedicle groove and 
foramen or for a distance of about 2 mm. Sides straight and steep, forming 
an angle of 95°. Pedicle slit about 1.5 mm. in length, narrow and confined to 
the convex area posterior to the beak. Surface marked by fine, elevated, evenly 
spaced ridges, about 8 to the millimeter at the front margin. 
Measurements in mm.—Holotype, length 9.7, width 8.0+, thickness 3.9. 
Types.—Holotype: 116801b; paratype: 116801a. 
Horizon and locality—Base of Athens formation (beds with Christiania) in 
Tennessee: 0.2 mile southeast of Britton Church, 24 miles northeast of Calhoun, 
Calhoun (T.V.A. 125-SW) Quadrangle. 
Discussion.—This species is characterized by the strongly convex postumbonal 
region and posterior slope and the deeply concave umbonal region. In these 
respects it differs from S. shuleri which it strongly resembles. 
SCHIZOTRETA SHULERI (Willard) 
Plate 19, B, figures 7-9; plate 21, D, figures 21, 22 
Acrosaccus shuleri Wiiarp, Bull. Mus. Comp. Zool., Harvard Coll., vol. 68, No. 6, p. 259, 
pl. 3, figs. 1, 2, 1928. 
Shell of about medium size for the genus; exterior marked by strong, even, 
elevated, concentric ridges increasing in size gradually on the margins; about 5 
ridges to the millimeter. Marginal ridges thickest on posterolateral edges. 
Pedicle valve forming a moderately high, asymmetrical cone with the apex 
located posterior to the middle. Posterior slope in lateral profile shorter than 
the anterior slope and steep; anterior slope less steep than the posterior one but 
considerably longer and very faintly convex; apical angle about 90°. Foramen 
not preserved, but indications point to its position just posterior to the apex; 
pedicle tube about 2 mm. long or slightly longer. 
Brachial valve almost circular and nearly flat; convex in the umbonal region 
but flattening anteriorly ; beak smooth, small, located about 0.5 mm. anterior to 
the posterior margin. 
Measurements in mm.—Pedicle valve (hypotype 109699a) : length 9.7, width 
9.5, thickness 3.9, posterior slope 5.0, anterior slope 8.0, lateral slopes 5.5; 
brachial valve (hypotype 109699c) : length 8.8, width 8.0. 
Types.—Lectotype: M.C.Z. 8581 (brachial valve) ; paratype: M.C.Z. 8591 
(pedicle valve) ; figured hypotypes: 109699a,c, 117969a,b. 
Horizon and locality.—Effna formation in Virginia: At McNutt Quarry, 12 
miles southwest of Bland, Burkes Garden (15’) Quadrangle. 
Rich Valley formation in Virginia: Porterfield Quarry, 5 miles east of Salt- 
ville, Maccrady (T.V.A. 218-NW) Quadrangle. 
Botetourt formation in Virginia: On the south side of the road, 0.2 mile east 
of Strasburg Junction, Strasburg (15’) Quadrangle. 
Discussion.—This species was based on two poorly preserved specimens which 
were thought to have relationships with Conotreta and its allies. The pedicle 
