804 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Figured specimens.—117548a,b; measured specimen: 117547. 
Horizon and locality—yYellow shaly limestone above 25-foot sandstone of 
Eureka group in Nevada: Saddle just north of hill 8167, Martins Ridge, 
Monitor Range, Roberts Mountains (1°) Quadrangle. 
Discussion—This species is suggestive of S. silicica nana in its possession of 
a fold and sulcus, but it has a much less swollen and less carinate pedicle valve, 
although one brachial valve is more deeply concave medially. 
Genus CHONETOIDEA Jones, 1928 
Chonetoidea Jones, Mem. Geol. Surv. Great Britain, Paleont., vol. 1, pt. 5, p. 393, 1928. 
CHONETOIDEA VIRGINICA Cooper, new species 
Plate 215, H, figures 30-33 
Shell small, wider than long with the hinge forming the widest part; cardinal 
extremities subacute; sides slightly oblique; anterior margin broadly rounded; 
multicostellate, costellae uneven in size; about 12 of the large ones may be 
counted at the front margin, but only 6 of these reach the umbo. Space between 
larger costellae marked by numerous fine threads. 
Pedicle valve gently convex in lateral and anterior profile; median region sub- 
carinate ; flanks somewhat flattened. Interior without dental plates but with a 
short, thin median septum occupying the delthyrial region. Muscle field small, 
diductor scars subparallel and short. Anterior margin marked by numerous short 
striae. 
Brachial valve flat to slightly concave in anterior and lateral profiles. Umbo 
concave; rest of valve nearly flat. Interior with short brachiophores, narrow 
and shallow notothyrial cavity and short median ridge located at about the middle 
of the valve. Lateral ridges in the form of elongate nodes or short ridges, 3 or 
more on each side of the median ridge and the inner 2 of them located close 
to the median ridge. Adductor field large. 
Measurements in mm.—Holotype, length 3.2, brachial length 2.8, midwidth 
4.3, hinge width 5.5, thickness ?. 
Types.—Holotype: 111097c; figured paratypes: 111097a,b; unfigured para- 
type: 1110974. 
Horizon and locality—Edinburg formation (Liberty Hall facies) in Virginia: 
From a bluff on the north fork of the Shenandoah River 4 mile above the south 
fork, opposite the bridge, Riverton, west of Front Royal, Front Royal (15’) 
Quadrangle. 
Discussion.—No other American species of this genus is now known to which 
this one can be compared. It differs from the British species C. papillosa (Reed) 
in having the costellae separated into fairly regular groups by the larger costellae, 
in having a nearly flat brachial valve, and in details of the brachial interior. 
ANISOPLEURELLA Cooper, new genus 
(Greek an, not; isos, equal; pleuron, rib) 
Shell small in all known species, wider than long with the hinge forming the 
widest part. Cardinal extremities acutely angular, often alate. Lateral profile 
