PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 541 
development of the fold and sulcus. Its closely crowded ornamentation is sug- 
gestive of O. costellata, but that species is more strongly ornamented and has 
a strong fold and sulcus. 
OXOPLECIA EIDSONENSIS Cooper, new species 
Plate 104, B, figures 7-11; plate 104, F, figures 32-38 
Shell of about medium size for the genus, transversely elliptical in outline, with 
narrowly rounded lateral margins and broadly rounded anterior margin. Pedicle 
valve fairly deep. Surface multicostellate with the fold occupied by 4 to 8 costellae 
and the sulcus by 3 to 7 costellae. Flanks marked by 12 costellae. Intercalation 
of costellae occurring just anterior to the umbo. Surface covered by concentric 
fila, about 4 to the millimeter on the flanks. 
Pedicle valve evenly and gently convex in lateral profile; anterior profile 
broadly convex but depressed medially by the sulcus. Beak slightly incurved. 
Sulcus originating just anterior to the umbo, about 24 mm. anterior to the end 
of the beak; sulcus moderately deep and widening rapidly to the front margin 
where it occupies about half the shell width. Costellae bounding sulcus stronger 
than others on flanks ; flanks gently convex but with steep slopes to the margins. 
Interarea apsacline; hinge equal to about half the valve width; deltidial ridge 
strongly elevated. Dental plates widely divergent. 
Brachial valve strongly convex in lateral profile with the maximum convexity 
in the umbonal region ; anterior profile strongly convex and with a median ele- 
vation formed by the fold. Umbo swollen; fold originating about 2 mm. anterior 
to the beak, low, rising slightly anteriorly and never strongly elevated; flanks 
inflated and with steep slopes. 
Measurements in mm.— 
Brachial Hinge f 
Length length Width width Thickness 
Pe Ee hia whos uci eer ae 5 13.0 11.9 15.9 10.1 10.6 
PARAL PED tonics cians tive ecw sle s 11.7 10.6 137, 7.9 8.2 
Types.—Holotype: 110847b; figured paratype: 110847a. 
Horizon and locality.—Lincolnshire formation in Tennessee: On old pasture 
road 4 mile northwest of Eidson, Kyles Ford (T.V.A. 170-SE) Quadrangle. 
Same formation in Virginia: 1 mile northeast of Jeff Gillespie’s house, 14.4 
miles southwest of Tazewell, Tazewell County. 
Discussion.—This species is characterized by a fairly strongly convex brachial 
valve and a moderately convex pedicle valve, a fairly deep pedicle sulcus but 
only a moderately elevated brachial fold. The species most closely resembles 
Oxoplecia planiventra but has a more convex pedicle valve and more robust form. 
Oxoplecia recta from the closely related Hogskin member of the Lincolnshire 
formation resembles O. eidsonensis more remotely than O. planiventra. O.xo- 
plecia eidsonensis is larger and more robust than the Hogskin species but it is 
also proportionately wider and more strongly elliptical in outline. 
