PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 255 
Type.—Holotype: 117973. 
Horizon and locality—Effna formation in Virginia: On the north side of 
Virginia Highway 114, 7 miles northeast of Lusters Gate, near Blacksburg, Va. 
Discussion.—This species suggests C. magna, depressa, and gigantea because 
of its large size. It differs from the first and last in its much less elevated conical 
form. It is more like C. depressa in its low conical profile but differs in having a 
narrower false interarea and a nearly plane brachial valve. 
SPONDYLOTRETA Cooper, new genus 
(Greek spondylium, vertebra; tretos, opening) 
Shell small, conical in profile, the cone flattened on the posterior side by a 
prominent and broad pseudointerarea. Surface marked by regular, strong con- 
centric elevated lines. 
Brachial valve with slightly postapical foramen; pedicle tube entering valve 
between a high median septum and the posterior inner surface ; pedicle tube con- 
tinued along wall as a forked ridge dying out about half the distance to the 
margin. 
Brachial valve gently concave in both profiles; moderately sulcate; hinge re- 
gion with a median triangular depression and thin, short plate anterior to it and 
overhanging the space between the hinge margin and the median septum. Median 
septum long, originating just anterior to the hinge margin and extending nearly 
to the front margin, triangular in profile with the apex of the triangle just pos- 
terior to the middle. Two large muscle marks occupy the posterolateral areas. 
Genotype.—S pondylotreta concentrica Cooper, new species. 
Discussion—This genus is quite unlike any of the others herein described in 
its septate pedicle valve. The strong median septum evidently serves the same 
purpose as the anteroapical callosity of Conotreta. 
Some uncertainty exists as to the assignment of this concave brachial valve to 
this genus, It is the only specimen like it recovered from this locality, and it is 
marked externally like the pedicle valves to which it is assigned. 
On the basis of its regularly concentric ornamentation Willard’s Conotreta 
declivis is assigned with doubt to this genus. The interior of Willard’s species 
is not known, and only two specimens occur in the National Collection. 
SPONDYLOTRETA CONCENTRICA Cooper, new species 
Plate 18, A, figures 1-7 
Shell small, conical in profile with the posterior side flattened ; surface marked 
by fairly strong, even concentric, elevated lines. 
Pedicle valve a misshapen cone in lateral profile with the posterior side flat- 
tened by the pseudointerarea ; anterior side gently convex ; apex bluntly pointed ; 
apical angle about 85°. Anterior profile with sides gently convex. Beak very 
slightly incurved and perforated by a small circular foramen. Pseudointerarea 
broad and flat ; intertrough not clearly defined. Interior with a long pedicle tube 
entering the valve just posterior to an erect and long median septum on the 
