700 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
about 3 mile north of Rye Cove; 1 mile northwest of Rye Cove, Clinchport 
(T.V.A. 188-NW) Quadrangle. 
Discussion.—This species is small and marked by fine costellae; it resembles 
S. compacta in form but is never so large, and is not so deep as the Benbolt 
species. Sowerbyella indistincta is like this species in size, but it has acute cardi- 
nal extremities in the adult whereas in S. parva the cardinal extremities are ob- 
tuse. Furthermore, the brachial valve of the Ward Cove species is more shallow 
than that of the Oklahoma species. 
SOWERBYELLA PERPLEXA Cooper, new species 
Plate 196, F, figures 30-44 
Shell of about medium size for the genus ; semielliptical in outline ; wider than 
long with the hinge forming the widest part; cardinal extremities auriculate ; 
sides oblique ; anterior margin broadly rounded; 2 large costellae in 1 mm. at the 
front margin; 3 to 5 fine costellae between the larger ones. Obscure oblique 
wrinkles on the posterior margins. 
Pedicle valve fairly evenly and moderately convex in lateral profile; anterior 
profile with median region rounded, not strongly elevated and with long gentle 
slopes. Valve swollen in the middle; umbo moderately inflated. 
Brachial valve most strongly concave just anterior to the umbo; concavity 
lessening anteriorly and laterally; posterolateral regions gently concave. 
Pedicle interior with narrow, deep, widely divergent diductor scars; median 
ridge short; brachial interior with delicate septa and often having the median 
septum unusually well developed. 
Measurements in mm.— 
Brachial Hinge 
Length length Midwidth width Thickness Height 
THOLOty pe eieie es « aieiciiens tater 6.2 5.4 9.7 II.0 13 2.2 
Paratype (117508c)... 5.2 4.7 7.8 9.1 1.0 1.6 
S Crrz7gegk)~.. ‘6.2 5.6 8.4 0.7 1.3 er 
i (117508E) .'.. P 8.0 12.5 12.5 ? ? 
Types.—Holotype: 117509a; figured paratypes: 117508b-g,i; unfigured para- 
types: 117508a,h,j-l, 117509b. 
Horizon and locality—Chatham Hill formation in Virginia: On north slope 
Walker Mountain, 1.2 miles S. 31° E. of Sharon Springs, Burkes Garden (15’) 
Quadrangle. 
Discussion —Sowerbyella perplexa has its fine costellae blocked out in definite 
bands by strong costellae, and the brachial valve is fairly deep. The species is 
most like S. negritus but differs in not having the costellae arranged in as broad 
bands as those of S. negritus and in not having a narrowly convex median region 
on the pedicle valve and a somewhat sulcate brachial valve. The Chatham Hill 
species also lacks the strong suggestion of plication on the pedicle valve of 
S. negritus. 
