830 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Pedicle valve roundly angulated at about the middle in lateral profile ; posterior 
or visceral portion nearly flat in lateral profile; geniculate portion somewhat 
broadly rounded; trail long and gently convex in profile. Umbo somewhat nar- 
rowly rounded; median portion of visceral region convex but flanks somewhat 
depressed. Posterior margin irregularly wrinkled. Interarea long; pseudodel- 
tidium thick and convex. Muscle area small. 
Brachial valve deeply concave, most concave in the median region where the 
valve geniculates; umbo and median region of the visceral part sulcate; flanks 
bounding sulcus flattened. Posterior margin wrinkled. 
Measurements in mm.—Holotype, length 21.0, brachial length 18.3, midwidth 
24.9, hinge width ?, thickness 3.1, surface length 28.0, trail length 14.0. 
Types.—Holotype: 1175914; figured paratypes: 117591b,d, 117592; unfigured 
paratypes: I1759QIc. 
Horizon and locality.—Lincolnshire formation (Hogskin member) in Ten- 
nessee: 0.4 mile east-northeast of Red Hill, 4 miles west-southwest of Thorn 
Hill, Avondale (T.V.A. 162-SW) Quadrangle; Sally Cleveland Farm, # mile 
southwest of Washburn, Dutch Valley (T.V.A. 154-SW) Quadrangle. 
Discussion.—Dactylogonia magna is an unusually large species for this genus 
which, besides its size, is characterized by an unsually long trail and a nearly 
square outline. It can only be compared to the larger species of the genus such 
as D. obsoleta (Butts) and D. obtusa. It differs from the former in larger size, 
square outline, longer trail, and more deeply concave brachial valve. From the 
latter it differs in its larger size, square outline, and the long, rounded trail. 
DACTYLOGONIA MAGNIFICA Cooper, new species 
Plate 225, A figures 1-4 
Shell of about medium size for the genus, thin shelled, generally wider than 
long and with the hinge forming the widest part; cardinal extremities acute; 
sides sloping obliquely toward the middle. Surface marked by strong costellae, 
2 or 3 in 5 mm. at the front which separate bands of closely crowded and beauti- 
fully cancellated costellae; fine costellae numbering about 7 to the millimeter at 
the front margin. 
Pedicle valve very gently convex in lateral profile but somewhat angulated in 
the front fifth; anterior profile broadly and gently convex and somewhat cari- 
nated in the middle; umbonal region slightly inflated, the swelling continued an- 
teriorly to the place of geniculation at the front as a low but poorly defined fold ; 
lateral slopes long and sloping gently to the sides. Foramen large, encroaching 
on the umbo; interior with large and flabellate muscle area. 
Brachial valve nearly flat to gently concave in profile and the anterior quarter 
bent in the direction of the brachial valve at a broad angle. Umbonal region 
sulcate. Interior with strongly developed and closely crowded adductor ridges. 
Measurements in mm.— 
Brachial Hinge 
Length length Midwidth width Thickness 
Holotype (pedicle valve) .......... 8.5 ? 11.4 12.9 > 
Paratype (brachial valve 117942c).. ? 8.7 12.0 12.8 ? 
