748 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Measurements in mm.— 
Brachial Hinge Surface 
Length length Midwidth width Thickness length Height 
HMolotypesy .2 isi. 2 9.8 8.3 II.9 12.4 3.8 13.5 5.0 
Paratype (117433g).. 9.7 ? 12.1 13.0 ? 12.0 3.4 
Types.—Holotype: 117433a; figured paratype: 117433b; unfigured paratypes: 
117433c-h. 
Horizon and locality—Oranda formation in Virginia: In the railroad cut 
4 mile west of Strasburg, Strasburg (15’) Quadrangle. 
Discussion.—This species is characterized by its medium size, strong, distant 
costellae, strong convexity, and the large size and considerable width of the 
muscle field of the pedicle valve. This species is marked somewhat like L. pul- 
chra, but that species is a much larger one. Leptellina abbreviata resembles 
smaller specimens of L. tennesseensis but differs markedly in the ornamentation 
particularly on the anterior portion of the valve. Leptellina delicatula is approxi- 
mately the same size as the Oranda species but is a squarer form with a much 
longer pedicle interarea than the Virginia species. Leptellina incompta and 
L. abbreviata are approximately the same age, but the Virginia species is much 
more convex than the Nevada one although the pedicle interiors are similar. 
LEPTELLINA BELLA Cooper, new species 
Plate 186, A, figures 1-8; plate 190, A, figures 1-4 
Shell small for the genus, wider than long, strongly concavo-convex; hinge 
forming widest part; cardinal extremities nearly rectangular, slightly auriculate. 
Lateral margins nearly straight ; anterior margin very broadly rounded. Surface 
multicostellate, costellae of 3 sizes. In young stages about 7 of the larger cos- 
tellae extending from the beak to the margin, but in adults addition of costellae 
of intermediate size in the front half increases the number of larger costellae to 
about 20 on each side of the median costella. The strongest of the costellae is 
the median one which is wider and more elevated than the others. The costellae 
of the 2 larger sizes are set in a field of very fine costellae about 15 in 1 mm. This 
figure includes 1 large costella. In addition to the radial ornamentation the sur- 
face of the posterior part of the valves particularly is marked by minute con- 
centric wrinkles. 
Pedicle valve moderately to strongly convex in lateral profile with the great- 
est convexity in the anterior half while the posterior half is only very gently 
convex; anterior profile highly arched. Beak protruding slightly posterior to 
the posterior margin; umbo swollen and elevated slightly. Lateral and anterior 
slopes very steep. Median region somewhat more swollen than the surrounding 
areas to form an ill-defined fold. Interarea moderately long, apsacline. 
Brachial valve deeply concave with the greatest concavity in the median por- 
tion ; region near cardinal extremities less concave. Umbonal region only gently 
concave. Interarea hypercline. Chilidium small. 
Interior: Muscle area of the pedicle valve deeply impressed, very small, hav- 
ing a length equal to about one-sixth that of the valve. Vascula media or main 
