896 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
larger ones. Costellae cancellated by fila. At the front margin of an adult 5 
of the larger costellae occupy a space of 5 mm. 
Pedicle valve with posterior slope moderately steep in lateral profile. Median 
region gently convex and anterior slope moderately steep but less so than the 
posterior slope. Umbonal and median region inflated ; lateral slopes steep. Slopes 
to cardinal extremities fairly gentle and slightly concave. Interarea short, nearly 
orthocline ; pseudodeltidium small. 
Brachial valve with concave umbonal region, lateral and median third of shell 
gently concave ; anterior and lateral marginal regions geniculated gently toward 
the brachial valve, thus accentuating the depth of concavity of the valve. Inter- 
area short, chilidium short and narrowly arched. 
Pedicle interior with short, widely divergent but well-defined ridges that ex- 
tend anterolaterally for a short distance around the posterolateral parts of the 
muscle area. Teeth unusually small for such a large shell. Muscle field large and 
flabellate. Median ridge not developed. 
Interior of brachial valve with the lobes of the cardinal process having short 
shafts but the myophore surface moderately broad and lobate on the edge toward 
the pedicle valve. Callus deposit about the delicate brachiophores very slight. 
Median ridge low; accessory ridges moderately well developed. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Foelatype tresa nd. + 2niisieaeuele 35.0 32.7 40.8 ? 30.2 6.8 
Paratype (117783b)....+..... 227 P 39.3 39.0 ? r 
Types.—Holotype: 117783a; figured paratypes: 117782a,b; unfigured para- 
types: 117782c, 117783b,c. 
Horizon and locality—Arline formation in Tennessee: At 4 mile south of 
McMullens, Meadow (T.V.A. 139-NW) Quadrangle; 4 mile southeast of 
Friendsville, Concord (T.V.A. 138-SW) Quadrangle; 54 miles southeast of 
Knoxville; 1 mile southeast of Fowlers Mill which is 10 miles south of Loudon, 
Loudon (30’) Quadrangle; 1 mile east-northeast of Friendsville, Louisville 
(T.V.A. 138-SE) Quadrangle. 
Discussion——Macrocoelia obesa is of moderate size for the genus, is strongly 
convex and fairly deeply concave. In these respects it resembles M. bella (for 
comparison see that species), M. champlainensis, and M. rotunda. The Tennes- 
see species differs from M. champlainensis in having more delicate ornamenta- 
tion, a more concave brachial valve, and a narrower hinge. Macrocoelia obesa 
differs from M. rotunda in its narrower hinge, much less convexity, and finer 
ornamentation. 
MACROCOELIA OCCIDENTALIS Cooper, new species 
Plate 233, D, figures 13-20 
Large, attaining a width of nearly 2 inches; hinge variable from wider than 
the midwidth to equal the midwidth ; cardinal extremities alate; sides subparallel 
to gently oblique; anterior margin broadly rounded; costellae strongly differ- 
