346 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
Measurements in mm.— 
Brachial Hinge 
Length length Width width Thickness 
Eloloty pe Cl RS Ue ED EG AS RES 13.4 my 15.3 14.4 5.8 
Banatype TOES) |. a3 sis dw sceicsnid oe = 12.8 10.6 14.4 13.0 5.9 
- (pedicle valve I116912a)... 19.9 ? 21.8 19.6 7.0 
% (brachial valve 116912c).. ? 15.1 20.9 18.5 28 
Uy (EIGOOEAN oe ce see eee 9.6 7.8 10.5 10.4 5.3 
zs (pedicle valve 109906b)... 12.0 P 12.6 11.4 4.7 
ce (brachial valve 109906a).. ? 10.6 13.3 12.4 1.4 
n (THOOTAN pepe 20s ads cata 15.2 12.5 15.9 13.1 8.4? 
Types—Holotype: 1099274; figured paratypes: 71965b, 109906c,g-i, 109927D, 
109928a,f, 116909a-d, 116912a-c, 116914; unfigured paratypes: 71965a, 10ggO6a, 
b,d-f,j-l, 109927c-1, 109928b-e,g. 
Horizon and locality——Ridley (?) formation in Georgia: On U. S. High- 
way 27, I mile north of Rock Spring, Nickajack (T.V.A. 113-SW) Quadrangle. 
Wardell formation and Wardell part of Dryden formation in Tennessee: 0.3 
mile southwest of Little Barren Church on old Tennessee Highway 33, Powder 
Springs (T.V.A. 154-SW) Quadrangle; south of side road 1 mile northeast of 
Watergap south of Bray, Swan Island (T.V.A. 162-NE) Quadrangle; Evans 
Ferry section (Hesperorthis bed) on Tennessee Highway 25E, 4 mile northeast 
of Indian Creek, Howard Quarter (T.V.A. 162-NW) Quadrangle; Clinch 
River, 12 miles northeast of Liberty Hill probably in Howard Quarter (T.V.A. 
162-NW) Quadrangle=Evans Ferry section; quarry 4 mile northeast of the 
depot at Clinton, Clinton (T.V.A. 137-SW) Quadrangle, Jacksboro, Jacksboro 
(T.V.A. 136-SW) Quadrangle; north of the Canyon of Gap Creek, 14 miles 
west of Arthur, Cumberland Gap (T.V.A. 153-SW) Quadrangle. 
Ridley formation in Tennessee on the east side of Marshall Knobs, 5 miles 
south of Murfreesboro, Murfreesboro (15’) Quadrangle ; 0.6 mile south of Chap- 
pel Hill Methodist Church on Tennessee Highway 28, 1 mile south of its junc- 
tion with Tennessee Highway 8, Sequatchie County, Daus (T.V.A. 104-SW) 
Quadrangle. 
Wardell formation and Wardell part of Dryden formation in Virginia: North 
quarry on Station Creek, 4 mile south of U. S. Highway 58, 2 miles east of Cum- 
berland Gap, Wheeler (T.V.A. 153-SW) Quadrangle; Lloyd Carter’s barn, 0.8 
mile by road northeast of brick school at Rye Cove, Clinchport (T.V.A. 188- 
NW) Quadrangle. 
Discussion.—This species is characterized by its nearly flat brachial valve, 
fairly convex pedicle valve and the inconspicuous brachial sulcus. It approaches 
H. tricenaria in size, especially the large specimens occurring at Station Creek 
near Cumberland Gap in southwestern Virginia. Generally the species is some- 
what smaller with a somewhat subcircular outline. 
HESPERORTHIS BICONVEXA Cooper, new species 
Plate 51, A, figures 1-6 
Shell large for the genus, one-sixth wider than long with slightly obtuse cardi- 
nal extremities. Sides gently rounded; anterior margin broadly rounded. Sur- 
