704 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
occur. Strangely, these specimens usually have the brachial valve crushed onto 
the inside of the pedicle valve so that the posterior part of the two valves is frozen 
together. The brachial valve must have been a more delicate shell than the 
pedicle one. 
PALAEOSTROPHOMENA RESUPINATA Cooper, new species 
Plate 167, A, figures 1-28 
Shell large, semielliptical in outline, wider than long with the hinge forming 
the greatest width. Lateral margins gently convex; anterior margin fairly 
strongly convex. Surface multicostellate, costellae of varying sizes, 11 of the 
larger ones occupying a space of 5 mm. at the front margin. 
Pedicle valve convex in the front half in lateral profile but concave in the an- 
terior half. Beak broadly obtuse, scarcely protruding posterior to the posterior 
margin. Umbonal and posteromedian region swollen. Valve geniculated gently 
in the direction of the pedicle valve about 7 mm. anterior to the beak. Geniculated 
half gently concave, the maximum concavity extending around the swollen por- 
tion from the middle of the valve to the posterior margin. Cardinal extremities 
flattened slightly, interarea long, strongly apsacline. Delthyrium covered by a 
narrow, convex pseudodeltidium. 
Brachial valve gently concave in the umbonal region and for a radius of about 
6 to 7 mm. anterior to it. Anterior portion of the valve moderately convex ex- 
cept in the posterolateral areas where it is slightly concave just anterior to the 
cardinal extremities. The interarea short, flat, hypercline. 
Interior of pedicle valve with most of interior occupied by a large and deeply 
impressed muscle field. Adjustor scars long and slender; diductor impressions 
reaching anterior to the middle; posterolateral margin of muscle field with more 
or less well developed marginal ridge; vascula media located at anterior end of 
diductor scars; secondary trunks deeply impressed ; adductor track elevated and 
thickened. 
Brachial interior with short brachiophores supported by a lateral thickening 
of the notothyrial platform; median ridge narrow, moderately elevated and ex- 
tending anterior to the middle; cardinal process with thick shaft ; myophore with 
elevated median crest. Pallial and ovarian impressions strongly marked. 
Measurements in mm.— 
Brachial Hinge 
Length length Midwidth width Thickness 
FIOLOEY Pei ee css cee eee ee cies « 17.6 17.3 20.5 20.7 5.0 
Paratype '(111069a) 0608 0. 16.7 16.1 20.7 23.4 3.6 
§ (ai7e77d)% eter) he 11:2 10.5 14.3 15.8 2g 
sf Bie 25 (02 14.7 13.7 18.2 ig he 28 
é CE242400) 0c se yee Se 13.0 12.6 16.7 17.9 2.9 
Types.—Holotype: 117377h; figured paratypes: 111069a, 111078c,d, 1173774, 
c-g; unfigured paratypes: 111069b, 111078a,b,e, 117377b, 123249a-c. 
Horizon and locality—Benbolt formation (lower) in Virginia: Just east of 
meridian 1730”, east of Moccasin Creek, on north edge of Mendota (T.V.A. 
