PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 519 
ATELELASMA DORSOCONVEXUM Cooper, new species 
Plate 80, G, figures 35-39; plate 82, M, figures 53-57 
Of about medium size for the genus, length-width relation variable; cardinal 
extremities nearly a right angle; sides gently rounded; anterior margin broadly 
rounded. Surface multicostellate with about 2 costellae in a millimeter at the 
front margin. 
Pedicle valve hemipyramidal with a moderately long interarea inclined in a 
catacline or strongly apsacline position. Lateral profile very slightly convex. 
Interior with spondylium short and shallow, septum unusually short. Pallial 
impressions not strongly impressed. 
Brachial valve gently convex in lateral profile with the maximum convexity in 
the posterior half. Median sulcus shallow and narrow but extending from the 
umbo to the middle. Flanks gently convex. Interior with notothyrial platform 
not strongly thickened; median ridge low and slender and extending nearly to 
the middle ; cardinal process slender. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width 
Holotype (pedicle valve) ............. 15.1 ? 17.7 15.8 
Paratype (pedicle valve 11701Id)...... 15.8 ? 15.7 14.0 
is (brachial valve 1170II1e)..... ? 14.2 17.9 14.0 
x (cs a, SEETOLTE) conc P 12.3 16.9 13.1 
Types.—Holotype: 117011h; figured paratypes: 110128b, 110129a-d, 11701Ib, 
d-f; unfigured paratypes: 110128a,c,d, 11701 Ia,c,g,i,j. 
Horizon and locality—Basal Athens formation in Tennessee: 24 miles south- 
east of Riceville, Calhoun (T.V.A. 125-SW) Quadrangle; 600 feet S. 40° E. 
of the railroad intersection with the highway 1 mile northeast of the courthouse 
in Athens, Athens (T.V.A. 125-NE) Quadrangle. 
Discussion—This species differs from A. perfectum in its smaller size, rela- 
tively greater width to length, shallower and shorter spondylium, more strongly 
sulcate and more convex brachial valve, and finely costellate exterior. Most of 
the specimens come from leached limestone taken from the road and bank near 
the intersection 24 miles southeast of Riceville. The specimens all occur in the 
form of impressions of the interior and exterior in a rock that is difficult to 
harden. Consequently, no replicas of the interior and exterior surfaces were 
prepared. The fairly strongly convex brachial valve seems to be a very charac- 
teristic feature of the species. 
Pallial marks are fairly well displayed in the specimens figured, but those of 
the pedicle valve are not as well developed as those of the opposite valve. The 
pedicle vascula media are not long. This is a consequence, no doubt, of the very 
short median septum supporting the spondylium. The brachial valve shows 2 
wide pallial trunks originating at the inside anterior of the adductor field. 
