714 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
posterolateral regions flattened. Beak small and protruding slightly beyond the 
posterior margin. Interarea flat, short, with narrowly rounded pseudodeltidium. 
Brachial valve gently concave in lateral profile ; umbo concave, small ; posterior 
part of valve nearly flat to very gently concave; median region slightly concave. 
Lateral and posterolateral regions flattened. Interarea short, anacline to hyper- 
cline. Chilidium moderately large. 
Interior of pedicle valve with moderately deep delthyrial cavity; dental plates 
mere remnants, divergent, with anterior ends thickened into false plates extend- 
ing anteriorly around the outside margins of the muscle field. Teeth small, simple. 
Muscle field small, narrow ; diductor impression elongate, narrow, extending far 
anterior to the front of the delthyrial chamber. Adductor impressions confined 
to delthyrial chamber and placed far back, separating the posterior ends of the 
diductor impressions. 
Brachial valve with cardinal process having a strong median carina and smaller 
lateral accessory septa. Chilidium projecting over posterior half of cardinal 
process; cardinal process protruding in the direction of the pedicle valve and 
overhanging thickened area posterior to median septum. Brachial processes thin, 
short, widely divergent. Median septum short, thin, elevated at its anterior end. 
Adductor field subflabellate. 
Measurements in mm.— 
Hinge 
width 
Length Width Thickness 
Eolotype'. IOP PROU IGA, BR 22.3 29.9 31.4 ? 
Paratype: (12g250a) 263), oss. <4 1221? 15.8 ? 22.7 ? 
Types.—Holotype: 117383a; figured paratypes: 117385b, 117386a-d, 
117387a-g, 123248a,b, 123250b; unfigured paratypes: 117383b-l, 117384a-e, 
117385a, 123250a,c-g. 
Horizon and locality.—Effna formation in Virginia: At Porterfield Quarry, 
5 miles east of Saltville, Maccrady (T.V.A. 218-NW) Quadrangle; McNutt 
Quarry, 12 miles southwest of Bland, Burkes Garden (15’) Quadrangle ; 2 miles 
northwest of Brownsburg, Lexington (15’) Quadrangle. 
Effna-Rich Valley formations in Virginia: At Porterfield Quarry, 5 miles 
east of Saltville, Maccrady (T.V.A. 218-NW) Quadrangle. 
Edinburg formation (Liberty Hall facies) in Virginia: 1.8 miles S. 4° W. of 
Bethel Church, 5.9 miles east of Harrisonburg, Harrisonburg (15’) Quadrangle. 
Pratt Ferry formation in Alabama: 0.2 mile southeast of Pratt Ferry, Blocton 
(15’) Quadrangle. 
Botetourt formation in Virginia: At the junction of Virginia County High- 
ways 731 and 724, 2 miles northwest of Brownsburg, Lexington (15’) Quad- 
rangle. 
Discussion —This species is based on few adult specimens. Most of the ma- 
terial consists of young forms some of which have been dissolved out of lime- 
stone and show the interiors to perfection. The adult is characterized by rather 
distant strong costellae at the front margin and a modest wrinkling on the pos- 
terior margin near the umbo. In G. musculosa the ornamentation has more 
