826 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Types.—Holotype: 11758ic; figured paratypes: 117581a,b,d,e, 117582a,b. 
Horizon and locality—Lenoir formation (reefy calcarenite beds under the 
Mosheim limestone) in Tennessee: On the southwest side of the cemetery be- 
hind the Friends Church, northwest edge of Friendsville, Concord (T.V.A. 
138-SW) Quadrangle. 
Lenoir formation (granular beds above the Mosheim limestone) in Tennessee: 
At Bluff City, Bluff City (T.V.A. 198-NE) Quadrangle; south of Friends 
Church, northwest side of Friendsville, Concord (T.V.A. 138-SW) Quadrangle. 
Tumbez formation in Virginia: In a small quarry on the south side of U. S. 
Highway 11, 3 miles southwest of Marion, Marion (T.V.A. 218-SE) Quad- 
rangle. 
Discussion—This species has generally been mistaken in the Southern Appa- 
lachians for D. incrassata (Hall). It is characterized by fairly large size for the 
genus and fairly strong geniculation. This species differs from D. incrassata in 
having a much larger size, in having a longer visceral disk region, somewhat 
less strong geniculation and a shorter trail. It differs strongly from D. genicu- 
lata in having a less rectangular outline, stronger costellae, and a less strongly 
geniculated trail. 
DACTYLOGONIA CONCENTRICA Cooper, new species 
Plate 216, B, figures 5-7 
Small, semielliptical in outline, hinge about equal in width to the width of the 
valve at the middle; cardinal extremities approximately a right angle; sides 
gently rounded; anterior margin broadly rounded. Surface marked by about 
II prominent thin, rounded costellae separating groups of very fine elevated cos- 
tellae that are crossed by fine elevated concentric lines of about the same strength 
as the fine costellae producing a beaded effect. Ornamentation of brachial valve 
showing a slightly stronger development of the concentric lines. 
Body of pedicle valve gently convex in lateral profile and very gently convex 
in anterior profile; geniculation of the pedicle valve taking place slightly less 
than 8 mm. anterior to the beak; angle of geniculation about 100°. Geniculated 
area short. Palintrope broad; interarea long and flat; pseudodeltidium strongly 
convex. Apical foramen small. 
Brachial valve gently concave with the greatest concavity appearing as a pit 
just anterior to the umbo. Anterior geniculation slight, resulting in a valve of 
nearly uniformly gentle concavity. When the shell is moistened the sutures of 
the adductor plates with the floor of the valve are visible. 
Measurements in mm.—Holotype, length 8.5, surface length 10, body length 8, 
length of gen. area 2, width 11.7, hinge width 11, thickness 3.6. 
Type.—Holotype: 117583. 
Horizon and locality Lincolnshire formation (Hogskin member) in Ten- 
nessee: 2 miles northeast of Hall Crossroad, Fountain City (T.V.A. 146-SW) 
Quadrangle. 
Discussion.—This is a small species characterized by subrectangular outline, 
