834 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
DACTYLOGONIA PARVA Cooper, new species 
Plate 218, A, figures 1-3 
Small for the genus, subtrapezoidal in outline and with the hinge forming the 
widest part. Sides gently rounded and oblique ; anterior margin broadly rounded ; 
surface marked by strong and fine costellae, the former not well developed ; con- 
centric wavy lines cancellate the fine costellae and generally dominate the orna- 
mentation. Visceral region marked by discontinuous concentric wrinkles espe- 
cially near the place of geniculation. 
Pedicle valve geniculating about 5 mm. anterior to the beak; angle of genicu- 
lation abrupt, approximately go°. Visceral region marked by a poorly defined, 
low median fold; flanks bounding fold concave; anterior of visceral region 
marked by a more or less prominent concentric fold. Trail long, gently convex 
in lateral profile. 
Brachial valve with visceral region gently concave; umbonal region concave} 
lateral areas of visceral region somewhat flattened. Trail abruptly geniculated. 
Measurements in mm.— 
Brachial Hinge Surface Trail 
Length length Midwidth width Thickness length length 
Holdoty pers. «setae 6.6 ? 8.1 9.6 ? 8.5 4.5 
Paratype (117597c). 6.5 5.2 8.7 9.8 1.6 7.5 2.0-+ 
Types——Holotype: 117597a; unfigured paratypes: 117597b-e. 
Horizon and locality—tLincolnshire formation (Hogskin member-Oligo- 
rhynchia bed) in Tennessee: 0.4 mile east-northeast of Red Hill, 4 miles west- 
southwest of Thorn Hill, Avondale (T.V.A. 162-SW) Quadrangle. 
Discussion—This species is characterized by its small size, wrinkled visceral 
region, and long, abruptly geniculated trail. Part of this characterization immedi- 
ately suggests D. palustris, but that species is a larger one, with a shorter and 
less strongly geniculated trail. 
DACTYLOGONIA PRONA (Willard) 
Leptaena prona Wirarp, Bull. Mus. Comp. Zool., Harvard Coll., vol. 68, No. 6, p. 270, 
pl. 3, figs. 15, 16, 1928. 
Type—Holotype: M.C.Z. 8620. 
Horizon and locality.—Lincolnshire formation (Dinorthis atavoides zone) in 
Virginia: Near Goodwins Ferry on New River, Giles County. 
Discussion.—The specimen on which this species is based is a very imperfect 
one with one side missing. Dimensions in millimeters based on the half dimen- 
sion are; length 14.3, midwidth 18.2, hinge width 25.8, surface length about 20, 
length of trail about 7.0. The angle of geniculation is about 95°. The species is 
thus a fairly large one having a moderately but sharply bent trail. The antero- 
median region of the trail is somewhat concave, in this respect resembling 
D, transversa. It differs, however, in much larger size and more sharply genicu- 
lated trail. Its very sharply geniculated anterior also distinguishes it from 
D. obsoleta, another Lincolnshire species. 
