PART. CHAZYAN AND RELATED BRACHIOPODS—COOPER 825 
sloping inward, anterior margin broadly rounded. Concavo-convex in lateral 
profile with both valves geniculated strongly in the direction of the brachial valve. 
Surface finely costellate, usually without concentric wrinkles. 
Pedicle valve with long palintrope, covered delthyrium, strongly convex 
pseudodeltidium and apical foramen. Muscle field moderately large with fairly 
long and wide diductor scars. Adjustor impressions present and adductors at- 
tached to a low median elevation. Internal surface tuberculate. 
Brachial valve with small cardinal process composed of 2 short-shafted pieces 
with myophore surfaces each receiving a pair of muscles; median ridge low or 
obsolete; brachial processes flat blades supported by the callus swelling of the 
notothyrial and muscle regions ; adductor field fairly small, marked by 4 blade- 
like plates arising from the floor, the smaller 2 between anterior and posterior 
adductor scars and the larger 2 on the inside of the anterior scars. Line of genicu- 
lation marked by a low, thickened ridge; entire inner surface tuberculate. 
Genotype-—Dactylogomia geniculata Ulrich and Cooper, Journ. Paleont., 
vol. 16, No. 5, p. 624, pl. go, figs. 19-23, 1942. 
Discussion.—Dactylogonia differs from Leptaena in the absence of concentric 
wrinkles in the visceral portion, but more importantly in the presence in the 
brachial valve of the bladelike ridges arising from the floor between the muscle 
scars and in the small median ridge. Members of this genus occur in the Chazy 
(Crown Point and Valcour) formations of New York and in several formations 
of the Southern Appalachians of Tennessee and Virginia, and in the Bromide 
formation of Oklahoma. 
DACTYLOGONIA ALTERNATA Cooper, new species 
Plate 218, D, figures 11-14; plate 218, G, figures 22-30 
Shell of about medium size for the genus, wider than long and with the hinge 
forming the widest part ; sides gently rounded; anterior margin broadly rounded; 
geniculation taking place about 8 mm. anterior to the beak; angle of geniculation 
about 100°. Surface marked by fine and coarse costellae, about 5 or 6 of the 
former occupying a space of 5 mm. at the front margin and up to 7 fine costellae 
between the stronger ones. 
Pedicle valve with visceral region flat to slightly concave in lateral profile; 
geniculated part narrowly rounded; trail short and gently convex in profile; 
foramen moderately large; interarea long; pseudodeltidium large. 
Brachial valve with visceral part nearly flat to faintly convex; trail short and 
fairly abruptly bent. 
Measurements in mm.— 
Brachial Mid- Hinge Thick- Surface pie en 
Length length width width ness length trail 
PA GIOCY Fes gac\ arash, idaiete 11.8 10.0 15.4 13.5+ 4.6 16.0 7.0 
Paratype (117581a).... 12.5 ? 075 18.0 ? 16.0 7.0 
(117581b).... 10.3 8.8 14.0 14.0 2.2 EES 3.0 
a (117581e).... 10.6 90.5 16.4 16.9 4.1 14.0+ 5.0-+ 
