898 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Measurements in mm.—Holotype, length 27.5, brachial length 25.2, midwidth 
36.4, hinge width 41.2 +, thickness 6.4. 
Types.—Holotype: 117789c; figured paratypes: 117788a, 117789a; unfigured 
paratypes: 117788b-d, 117789b. 
Horizon and locality—Little Oak formation in Alabama: At the junction of 
Bailey Gap and Cahaba Valley roads, SWiSW3 sec. 13, T. 19 S., R. 2 W., 
13 miles northeast of Newhope Church, Vandiver (15’) Quadrangle. 
Discussion—tThis species has strongly marked ornamentation, the larger cos- 
tellae standing out prominently in a mat of finer ones. The species has moderate 
size and moderate convexity. It is larger and more strongly ornamented than 
M. elegantula. It is wider and less convex than M. obesa and is smaller and 
more elegantly ornamented than O. occidentalis. Another feature of this species 
not seen on any other member of the genus is the flattening or even slight con- 
vexity of the posterior third of the brachial valve. This feature is pronounced 
on the holotype. 
MACROCOELIA PLATYS Cooper, new species 
Plate 231, A, figures 1-7 
Shell of about medium size for the genus, wider than long; hinge equal to or 
narrower than the midwidth; sides gently convex, slightly oblique; anterior 
margin strongly rounded ; costellae alternating strong and fine, 3 or less of the 
latter alternating with the stronger ones; 3 costellae to the millimeter at the 
front margin. 
Pedicle valve moderately convex in lateral profile and with the maximum 
convexity at the middle; anterior profile broadly and moderately domed; umbo 
narrowly swollen and forming a low fold that extends anteriorly nearly to the 
middle; median region moderately swollen; anterior slope long and gentle; lat- 
eral slopes shorter and steeper than the anterior one. Pseudodeltidium short; 
interarea moderately long. Muscle field heart shaped, moderately large. 
Brachial valve nearly flat to gently concave in lateral profile; most concave in 
the median region but becoming shallow to flat toward the margins. 
Measurements in mm.— 
Brachial Hinge 
Length length Midwidth width Thickness 
Holotype seus sessieet a Ball! 32.8 30.8 38.4 34.3 6.0 
Paratype ot UUZ7GOd) MFA escuree4 32:2 ? 37.6 30.9 ? 
Types.—Holotype: 117790a; figured paratypes: 117790b,c; unfigured para- 
types: 117790d-l. 
Horizon and locality—Lincolnshire formation in Tennessee: At Marble Bluff, 
8 miles west-northwest of Loudon, Loudon (30’) Quadrangle. 
Discussion.—This species is characterized by moderate size and low convexity 
and an almost flat brachial valve. In these respects it is like M. occidentalis, but it 
is smaller and flatter than that species. It is very similar to the young of 
M. duplistriata, and more extensive collecting may ultimately prove them to be 
the same. 
