828 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Surface covered by closely crowded costellae of unequal size, 5 to 9 of the smaller 
costellae arranged into groups by the scattered larger ones. 
Pedicle valve with the posterior 9 mm. nearly flat but the anterior narrowly 
convex; geniculation takes place at about 9 mm. anterior to the beak and the 
angle of geniculation is about 95°. Beak erect, the umbo inconspicuous but 
slightly swollen. Geniculated part narrowly convex; front slope slightly convex 
in profile and steep. 
Umbo of brachial valve forming a round hollow anterior to the beak ; body of 
valve slightly concave but flattened somewhat at the cardinal extremities. Genicu- 
lated part fitting closely against the trail of the pedicle valve and having practi- 
cally the same contour as that valve. 
Interior of pedicle valve with muscle field not quite extending to the middle, 
moderately impressed; adductor ridge low. Brachial valve with short median 
septum situated between the lobes of the cardinal process; adductor blades 
strongly developed ; ridge at front of visceral area slightly elevated, moderately 
thick. 
Measurements in mm.— 
Brachial Hinge Thick- Surface 
Length length Midwidth width ness length 
Holetype” ss: sc. s eee II.I 0.8 15.0 16+ 3.0 15.0 
Paratype (108202e)... 10.2 9.8 14.7 16-+ 2.9 14.5 
o (108202f) ... I1.1 10.2 15.8 ? 23 14.0 
Types——Holotype: 108202a; paratypes: 108202b-g; figured hypotypes: 
117585b,c,f,h, 117586a, 117587, 117588a. 
Horizon and locality.—Arline formation in Tennessee: Along old wagon road 
in glade, 4 mile southeast of Friendsville, Concord (T.V.A. 138-SW) Quad- 
rangle; 4 mile south of McMullens, Meadow (T.V.A. 139-NW) Quadrangle. 
Arline formation in Virginia: Porterfield Quarry, 5 miles east of Saltville, 
Maccrady (T.V.A. 218-NW) Quadrangle. 
Little Oak formation in Alabama: Junction of Bailey Gap and main roads, 
1} miles northeast of Newhope Church, Cahaba Valley, SW4SW4 sec. 13, 
T. 19 S., R. 2 W., Vandiver (15’) Quadrangle. 
Discussion.—This species can be recognized by the similarity of its outline and 
profile to examples of Leptaena. The outline is nearly rectangular and the an- 
terior geniculation is abrupt. No other described species except D. prona and 
D., transversa, is quite like it in these respects. D. prona (Willard) is suggestive 
but that species is much larger and the trail is marked by a distinct sulcus. 
Dactylogonia transversa is strongly rectangular in outline and is abruptly genicu- 
late, but it is a larger and proportionately wider shell than D. geniculata. 
DACTYLOGONIA INCRASSATA (Hall) 
Plate 219, I, figures 16-23; plate 210, J, figures 24-27; plate 220, B, figures 6-8; 
plate 226, C, figures 5-9 
Leptaena incrassata HALL, Pal. New York, vol. 1, p. 19, pl. 4 bis, figs. 2a-d, 1847—-RAYMOND, 
Ann. Carnegie Mus., vol. 7, No. 2, p. 230, pl. 34, figs. 32-37, IOII. 
Shell fairly large for the genus, wider than long, with the hinge width almost 
twice the length ; cardinal extremities alate; strongly geniculate; angle of genicu- 
