602 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Mount Hagan School, southeast corner of the northeast subquad., Hilton (T.V.A. 
197-NW) Quadrangle. 
Discussion—This species is most similar to small, strongly costate specimens 
of P. aseptata but differs in the greater depth of the sulcus and in the extravagant 
development of the anterior ends of the costae bounding the sulcus. 
PLECTOCAMARA TRANSVERSA Cooper, new species 
Plate 122, F, figures 35-37 
Shell large for the genus, wide, with gently oblique posterolateral margins 
forming a broadly obtuse apical angle. Sulcus originating at the beak, deep and 
moderately wide, occupied by 2 costae. Flanks flattened to gently concave, de- 
pressed below the strong bounding costae of the sulcus, marked by 9 costae. Lat- 
eral profile gently convex. Spondylium short, deep, sessile at the posterior but 
elevated on a short median septum at the anterior. 
Measurements in mm.—Holotype, length 8.7, width 12.4. 
Type.—Holotype: 117188. 
Horizon and locality —Edinburg formation (lower part of Nidulites zone) in 
Virginia. On U. S. Highway 11, 100 yards south of Battlefield Crystal Caverns 
entrance, I mile north of Strasburg, Strasburg (15’) Quadrangle. 
Discussion.—This is the largest of the known species of this genus. Besides 
its size it is characterized by its great width and numerous costae. 
Subfamily STENOCAMARINAE Cooper, new subfamily 
Camerellidae having long, discrete, subparallel dental plates in the pedicle valve. 
STENOCAMARA Cooper, new genus 
(Greek steno, narrow; camara, chamber) 
Shell suggesting Camerella in outline and profile but not plicated except for 
fold and sulcus. Anterior commissure strongly uniplicate; hinge narrow; sur- 
face marked by concentric lines of growth only. 
Pedicle valve more or less strongly sulcate; beak small, somewhat incurved ; 
interarea small and narrow; interior with 2 long, subparallel dental piates defin- 
ing a long, deep, and very narrow delthyrial chamber. 
Brachial valve with incurved beak and strong median fold; interior charac- 
terized by a short V-shaped cruralium supported by a long and elevated median 
septum. 
Genotype.—Stenocamara perplexa Cooper, new species. 
Discussion—This genus is characterized by having subparallel dental plates 
in the pedicle valve and a cruralium in the brachial valve. Externally the genus 
suggests the syntrophids because of its smooth exterior and strongly uniplicate 
anterior commissure. The structure of the brachial valve is most like Xenelasma 
Ulrich and Cooper which occurs in the Nittany formation and its equivalents in 
Virginia, Tennessee, and Texas. Xenelasma is characterized by having dental 
