502 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
and meeting at the beak and an intercalated costa between the lateral 2 which 
bifurcates the branches extending to the anterior margin; flanks bounding fold 
gently swollen. Interarea long and strongly apsacline. 
Brachial valve slightly convex in lateral profile; interior profile broadly and 
gently convex; umbo gently swollen; fold originating on the umbo, shallow and 
narrow; occupied by 3 costae. Tongue broad. Flanks bounding sulcus gently 
inflated ; posterolateral areas flattened. 
Interior of pedicle valve with small teeth and broad and shallow free spondy- 
lium; brachial valve with broad and shallow notothyrial cavity, long brachio- 
phores, and prominent brachiophore plates. 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Holotype (pedicle valve) ......... 3.4 ? 5.3 6.4 ¢ 
Paratype (brachial valve 117086d).. ? 2.8 5.3 5.9 ? 
Types.—Holotype: 117086c; figured paratypes: 117086d,g; unfigured para- 
types: 117086a,b,e,f,h,1. 
Horizon and locality—Effna-Rich Valley formations in Virginia: At Porter- 
field Quarry, 5 miles east of Saltville, Maccrady (T.V.A. 218-NW) Quadrangle. 
Discussion.—This species is characterized by its large size and transverse 
form. In these respects it differs from all others herein described. It is also 
characterized by having a low fold and a shallow sulcus. This combination of 
characters makes it unique. 
SCAPHORTHIS Cooper, new genus 
(Greek scaphos, hollow) 
Subcircular to transversely subelliptical in outline; margins rounded ; anterior 
commissure rectimarginate or sulcate; biconvex in profile, the pedicle valve hav- 
ing the greater convexity ; brachial valve sulcate, sulcus usually shallow; hinge 
narrower than the greatest shell width which is at about the middle; surface 
multicostellate ; test fibrous, impunctate. 
Pedicle interior with open delthyrium or with delthyrium constricted slightly 
by lateral plates; delthyrial cavity deep; teeth small, sharp; fossettes moderately 
deep ; dental plates short, flaring ; muscle field orthoid in pattern, somewhat heart 
shaped in outline; diductor scars narrow; adductor track wide; anterior margin 
of muscle field slightly thickened and often with a low median callosity anterior 
to the anterior margin; vascula media divergent, many branched. 
Brachial valve with deep but narrow delthyrial cavity; cardinal process with 
narrowly rounded shaft but thin and bladelike myophore; brachiophores short 
and stout but with fairly long, sharp points; brachiophores supported by stout 
plates that converge to the median ridge and unite with it; fulcral plates small; 
median ridge low, narrow, subcarinate, and extending to about the middle. Ad- 
ductor field small, anterior scars separable into pairs. 
Genotype.—Scaphorthis virginiensis Cooper, new species. 
