PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 247 
If this species does belong to Acrotreta, it is a fairly large form for the genus. 
It is characterized by its depressed conical form and the low convexity of the 
brachial valve. It is suggestive of Conotreta depressa but is a somewhat more 
elevated cone than that form. 
Genus CONOTRETA Walcott, 1889 
Conotreta Watcott, Proc. U. S. Nat. Mus., vol. 12, p. 365, figs. 1-4, 1890 (extracts 1889). 
The name Conotreta has long been known, but it has been applied to a single 
species in this country. A few other species are known in Europe, but until this 
study was undertaken the genotype was the only one known in this country. 
In the description of the genus, Walcott made known the pedicle valve only. 
Discovery of abundance of mineralized specimens in the Liberty Hall facies near 
Lacy Spring, Va., and the limestone at Pratt Ferry, Ala., makes it possible to 
describe and illustrate some fine interiors. 
The pedicle valve is an irregular cone, the posterior side of the cone flattened 
by the pseudointerarea but the anterior side usually convex. The posterior side 
with the pseudointerarea is usually shorter than the anterior side. The side fac- 
ing the brachial valve is thus oblique. The beak is small and usually smooth and 
slightly curved in a posterior direction. It may, however, be bent slightly an- 
teriorly as in C. plana described below. The foramen is minute and is located 
very slightly posterior to the apex. The pseudointerarea often is simply a flat- 
tened triangular area on the posterior face, ornamented in the same manner as 
the rest of the valve. More often, however, it shows a slightly elevated central 
track defined by shallow grooves down which a more or less shallow impressed 
line extends. This impressed line is the intertrough, and it may extend from the 
foramen to the margin or may be visible for a short distance only. Its function 
is uncertain. In exfoliated specimens the intertrough shows more clearly. In 
such specimens the median swollen portion of the palintrope is well shown and 
is bounded by 2 grooves that represent slight thickenings or depressions that help 
to support the portion of the palintrope that covers the pedicle region. 
The foramen, although minute, leads into a pedicle groove of considerable 
size that widens toward the brachial valve and opens into the interior posterior 
to a pillar or boss of vesicular shell used to strengthen the apical region as the 
valve grows. The pedicle aperture inside the valve is many times larger than the 
foramen. The base of the pedicle was probably attached to the posterior surface 
of the pillar. 
One of the features that gave Conotreta generic status is the great develop- 
ment in size and number of the pallial trunks in the pedicle valve. The 2 pri- 
mary trunks, corresponding to the vascula media of Opik, originate on each side 
of the pillar and by the depth of their insertion into the shell substance make 
the pillar stand into bold relief. The major trunks branch more or less numer- 
ously, chiefly by bifurcation, and may produce as many as 7 trunks on each side. 
The musculature of the pedicle valve is difficult to determine, but two speci- 
mens from the Liberty Hall facies show a pair of muscles located on each side 
of the valve posterolaterally to the pedicle groove. The larger scar is located 
farthest from the groove. One of these pairs probably corresponds to the cardi- 
