PART I CHAZYAN AND RELATED BRACHIOPODS—-COOPER 417 
Brachial valve having the greatest convexity in lateral profile somewhat an- 
terior to the middle, forming a low arch somewhat flattened at the middle in 
anterior profile. Umbo concave, with the concavity produced anteriorly as a 
very shallow and narrow sulcus to a point a short distance anterior to the middle. 
Median, anteromedian, and anterolateral areas moderately swollen with moder- 
ately steep slopes to the margins. Posterolateral slopes gentle. Interarea nearly 
as long as the pedicle one, gently anacline. 
Interior: Pedicle muscle area about as long as wide and in length equal to 
about a third the length of the valve. Adductor track wide, slightly elevated an- 
teriorly ; diductor impressions long and narrow. Pallial trunks not strongly im- 
pressed. Median ridge of brachial valve low and short, equal in length to about 
one-third the length of the valve. Cardinal process short and stout; myophore 
not greatly thickened. 
Measurements in mm.— 
Hinge Thickness 
Length Width width 
Hypotype (pedicle valve 110371d)...... 22.4 26.3 23.2 4.2 
‘ Cmio37ie) wisiiiuss Jute. vlc 23.7 26.7 22.8 5.4 
‘§ (brachial valve 110371a).... 24.3 27.3 23:2 5.5 
Types.—Holotype: M.C.Z. 8597; figured hypotypes: 110371a,b,d,e, 110372a, 
b, 116984h; unfigured hypotypes: 11037Ic, 116984a-g. 
Horizon and locality—Chatham Hill formation in Virginia: Grayson Farm, 
4 miles southwest of Bland, Bland County ; 1.2 miles S. 31° E. of Sharon Springs, 
Burkes Garden (15’) Quadrangle. 
Botetourt formation in Virginia: Near Dunkard Church, 7 miles west of 
Natural Bridge, Natural Bridge (15’) Quadrangle; junction Virginia Highways 
311 and 114, $ mile southwest of Catawba, Salem (15’) Quadrangle; about 1 
mile northwest of Lexington, Lexington (15’) Quadrangle; 14 miles southeast 
of Harrisonburg, Harrisonburg (15’) Quadrangle. 
Whitesburg formation in Tennessee: In the railroad cut at Summit Hill 
school, 1 mile southwest of Otes, Bulls Gap (T.V.A. 171-SE) Quadrangle. 
Discussion.—This species is known from a few specimens only: The holo- 
type, which is preserved in the Museum of Comparative Zoology, Harvard; a 
few fine valves etched out of black limestone; and a few exfoliated specimens 
preserved in black limestone. The species is characterized by its strongly bicon- 
vex form, a hinge narrower than the greatest shell width, and fairly strong 
costellae. This species most closely resembles M. convexa but differs in the nar- 
rower hinge, somewhat squarer form, and lesser development of the sulcus of 
the brachial valve. M. bursa differs from M. plicata in the lesser number of cos- 
tellae and possession of a smaller muscle area in the pedicle valve. Multicostella 
whitesburgensis Butts occurs at about the same horizon as M. bursa and has simi- 
lar exterior characters to that species. It is therefore placed as a synonym of 
Raymond’s species. 
