PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 599 
Discussion—tThis species differs from P. aseptata in having less numerous 
and less closely spaced costae, in having a less narrow umbo and less erect beak, 
in having little tendency for development of extra costae on the fold and the sul- 
cus, less costae on the flanks, and in having the fold originate nearer the middle. 
The two species are actually fairly similar, but no instances of 3 costae in the 
sulcus and 4 on the fold have been observed in P. costata. 
Like P. aseptata this species is also a very variable one, but the variations are 
not as extreme as in the Benbolt species. Generally, P. costata does not at- 
tain as large a size as P. aseptata, and the sulcus is not usually so deep. Further- 
more, the species is more conservative in its costation, the costae of the flanks 
remaining fairly constant. 
PLECTOCAMARA ERECTA Cooper, new species 
Plate 123, D, figures 17-21 
Shell of usual size for the genus, length and width about equal; outline sub- 
pentagonal ; posterolateral margins straight, lateral margins narrowly rounded; 
anterior margin truncated. Strongly uniplicate. Surface costate, with 3 costae 
on the fold, 2 in the sulcus, and 4 on the flanks. 
Lateral profile slightly convex but with a local inflation at the umbo; anterior 
profile faintly convex. Sulcus originating 2 to 24 mm. anterior to the beak, deep- 
ening anteriorly and terminating in a narrow, short tongue. Sides of sulcus pre- 
cipitous at the front. Costae bounding sulcus elevated and protuberant an- 
teriorly ; flanks flat and inclined fairly steeply. 
Brachial valve moderately convex in lateral profile, broadly and moderately 
convex in anterior profile; brachial valve slightly deeper than the pedicle valve ; 
umbonal region moderately inflated ; fold originating on the umbo but not ele- 
vated strongly throughout its length. Fold rounded in lateral profile; flanks 
moderately swollen and with steep slopes, not strongly depressed below the level 
of the fold. 
Measurements in mm.—Holotype, length 5.5, brachial length 5.1, width 5.9, 
hinge width 1.4, thickness 3.7. 
Type.—Holotype: 117183. 
Horizon and locality—Wardell formation in Tennessee: Northeast side of 
Lee Valley, Lee Valley (T.V.A. 171-NW) Quadrangle. 
Discussion.—This species is characterized by its erect form, the width and 
length being nearly equal, and by the sparse costation. It differs from P. aseptata 
in having less width, less costae, and a narrower fold and sulcus. Plectocamara 
erecta is also similar to P. costata in its costation, but it is not so wide, has a 
more swollen brachial valve, less elevated fold, and a narrower sulcus. 
Plectocamara is a rare genus in the Wardell formation. Consequently, the 
foregoing species is based on a single good specimen and one other exfoliated one 
which shows some details of the interior. 
