248 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
nal scar figured by Walcott in “Acrotreta.” Alabama specimens show large scars 
just inside the posterior margin on the underside of the palintrope. 
Brachial interior: The etched specimens from the Liberty Hall facies show 
the interior of the brachial valve to perfection. The posterior quarter is thickened 
to form a platform. At the apex a small triangular groove occurs that may have 
served as a seat of muscle attachment. Just anterior to the groove and at each 
angle occurs a large elliptical muscle scar. Inside these scars and at their anterior 
end appear 2 small muscle scars. At the anterior end of the thickened platform 
a thin elevated median ridge rises to a point slightly anterior to the middle and 
then descends rapidly to the floor of the valve. The 4 muscle scars are the only 
ones determined with certainty. It is possible that the median septum also was 
a seat of muscle attachment, but no marks were seen on it to bear out this 
suggestion. The large scars are the cardinals of Walcott, but no scars were seen 
anterior to the posterior platform that could be interpreted as the centrals of 
Walcott. 
Conotreta is common in the Botetourt and Pratt Ferry formations and the car- 
bonaceous limestones of the Liberty Hall facies in the belt between Harrison- 
burg and Winchester, Va. Only one species of Conotreta is so far known from 
pre-Botetourt rocks in the Appalachians. Elsewhere specimens having the outer 
form of Conotreta are referred to the genus Acrotreta. 
Conotreta cannot be regarded as a well-established genus until the internal char- 
acters of Acrotreta are thoroughly known. The latter occurs in rocks equivalent 
to those of the Black River-Trenton interval in Estonia, but its internal charac- 
ters are not clearly known. The bases of 2 pallial trunks are visible in one of 
the types, but the extent to which they branch is unknown. It is thus possible 
that Acrotreta and Conotreta are synonyms, but the point cannot now be settled. 
CONOTRETA ? ALTA Cooper, new species 
Plate 16, A, figures 1-3 
This species differs from all others known from Chazyan rocks by its very 
narrow form and the great elevation of the pedicle valve. This species has an 
apical angle of 30° and a lateral angle of 26°. It is thus the narrowest form 
known. The pseudointerarea is narrow, but the intertrough is located on a low, 
longitudinal elevation along the center of the pseudointerarea. Surface marked 
by very fine concentric lines. The holotype lacks the apex but is I.g mm. long 
along the anterior slope and 1.2 mm. long on the posterior face, width 1.7 mm. 
Type.—Holotype: 109715. 
Horizon and locality.—Arline formation in Tennessee: In glade 4 mile south- 
east of Friendsville, Concord (T.V.A. 138-SW) Quadrangle. 
CONOTRETA ? ALTIROSTRA Cooper, new species 
Plate 18, G, figures 51-53 
Shell small, long and slender, forming a slightly curved cone obliquely open 
at the anterior end. Pedicle valve a slender cone with gently curved posterior 
