444 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Holotype 278225. Renews 15.9 16.3 17.9 15.7? 8.3 
Paratype (117008a) ......... 15.5 15.5 17.9 18.9 8.0 
Types.—Holotype: 117007; figured paratypes: 117008a,b,f; unfigured para- 
types: 117008c-e. 
Horizon and locality—Ridley formation (lower third) in Tennessee: At east 
side of Marshall Knobs, 5 miles south of Murfreesboro, Murfreesboro (15’) 
Quadrangle. 
Discussion —This is a small and compact species characterized by a quad- 
rate form. It differs from all the other species with quadrate outline in its small 
size. Large specimens are suggestive of C. lebanonensis but differ in their squarer 
outline. The species is a rare one. 
CHAULISTOMELLA SUPERLATA Cooper, new species 
Plate 66, A, figures 1-9 
Shell subrectangular in outline, wider than long and with a variable hinge; 
sides gently rounded, slightly oblique ; anterior margin broadly rounded ; anterior 
commissure rectimarginate; lateral commissure deflected toward the brachial 
valve at the posterior ; surface multicostellate ; costellae uneven, about Io in 5 mm. 
at the anterior margin. 
Pedicle valve unevenly convex in lateral profile, the posterior third very gently 
convex, the anterior two-thirds moderately concave. Anterior profile gently con- 
cave. Umbo slightly swollen, subcarinate; fold narrow, fairly distinct in the 
posterior region but becoming less distinct anteriorly, then becoming still more in- 
distinct or obsolete; anterior two-thirds concave; flanks bounding concavity 
forming a fairly prominent oblique fold; posterolateral extremities strongly de- 
flected toward the brachial valve. Interarea long, catacline; muscle field deeply 
indented anteriorly, deeply impressed and with fairly large adjustor scars. Other 
pallial marks not distinctly impressed. 
Brachial valve moderately strongly convex in lateral profile with the most 
convex part in the posterior half; anterior half somewhat flattened. Anterior 
profile strongly convex medianly but with fairly long and moderately steep lateral 
slopes. Umbonal region swollen, sulcate ; sulcus shallow, distinct for two-thirds 
the valve length, becoming indistinct or obsolete in the anterior third. Median 
region swollen; lateral and umbonal slopes steep. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
ETOLOEY PEs wipigadslste oor. ARS 17.8 19.6 24.6 24.5+ 9.4 
Paratype (110506b) ......... 15.0 16.6 20.4 20.4 7.0 
Types.—Holotype: 110506a; figured paratypes: 110506b,d-f; unfigured para- 
types: 110506c,¢. 
Horizon and locality.—Ridley formation in Georgia: On U. S. Highway 27 
