594 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
edge of the brachiophore. This is similar to the structure of the brachial plates 
of Camerella. Perimecocoelia is thus a camerellid with elongate cruralium. 
The adductor field of Perimecocoelia, at least in the present species, is some- 
what thickened and is often surrounded by an elevated callus. The posterior scars 
are located beside the anterior end of the cruralium; the anterior scars, which 
are the larger, are located just anterior to the end of the cruralium and are sepa- 
rated by a low ridge extending anterior to the cruralium. 
PERIMECOCOELIA ELLIPTICA Cooper, new species 
Plate 111, C, figures 27-35 
Shell small, broadly triangular in outline, with low, inconspicuous beaks. 
Brachial valve slightly deeper than the pedicle valve. Both profiles narrowly 
lenticular. Paucicostate, the posterior half smooth and the anterior half strongly 
costate ; 2 costae in the sulcus, 3 on the fold, and 2 on the flanks ; fold low, defined 
by the 3 strongest costae slightly elevated at the anterior third. Sulcus shallow 
and wide, originating in the anterior third. 
Measurements in mm.—Holotype, length 7.0, brachial length 7.0, width 8.5, 
hinge width 1.7, thickness 4.7. 
Type.—Holotype: 111164. 
Horizon and locality—Arline formation in Tennessee: North side of old 
wagon road in cedar glade, + mile southeast of Friendsville, Concord (T.V.A. 
138-SW ) Quadrangle. 
Discussion.—This species is similar to P. semicostata but is smaller, with only 
2 costae in the sulcus and becoming costate at a less distance from the beak. The 
interior of the species is not known, but the elliptical outline, wide sulcus, and 
semicostate form all suggest reference to Perimecocoeha rather than Camerella. 
PERIMECOCOELIA SEMICOSTATA Cooper, new species 
Plate 108, E, figures 21-25; plate 114, C, figures 35-38; plate 117, E, figures 28-51; 
plate 117, F, figures 52-59; plate 119, B, figures 6, 7 
Parastrophia rotundiformis Wittarp (part), Mus. Comp. Zool., Harvard Coll., vol. 68, 
No. 6, p. 290, 1928. 
Shell transversely but broadly elliptical in outline; posterior margin broadly 
rounded ; lateral margins strongly rounded ; anterior margin somewhat truncated. 
Anterior commissure strongly uniplicate; posterior half smooth; anterior half 
costate with 3 (rarely 4) costae on the brachial fold and 1 to 3 obscure ones on 
the flanks; 2 costae (rarely 3) in the sulcus, and 2 to 4 poorly defined ones on 
the flanks. 
Pedicle valve unevenly convex in lateral profile, with the most convexity in 
the posterior region and with a strongly geniculated tongue; anterior profile 
slightly convex ; umbonal region gently swollen; sulcus originating slightly pos- 
terior to the middle, deepening and widening abruptly; sulcus bounded by 2 
subangular costae that die out with the sulcus posteriorly; flanks nearly flat, 
