PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 759 
ing that of the pedicle valve. Umbo sulcate, the sulcus being continued anterior 
to the front margin as a narrow, shallow depression. Flanks bounding sulcus 
broadly and gently concave transversely but narrowly and deeply concave longi- 
tudinally. Interarea short, hypercline ; cardinal process and chilidial plates small, 
fused into a single plate. 
Interior of pedicle valve with widely flaring dental plates. Interior of brachial 
valve with median septum reaching the point of maximum curvature and mod- 
erately elevated anteriorly but very low posteriorly. Edge of visceral area low 
and inconspicuous. 
Measurements in mm.—Holotype, length 9.2, brachial length 7.6, surface 
length 12.5, midwidth 20.9+, hinge width ?, thickness 2.8, height 4.5. 
Types.—Holotype: 117457a; figured paratype: 117457c; unfigured paratypes: 
117457b,d. 
Horizon and locality—Arline formation (near top) in Virginia: Near en- 
trance to Porterfield Quarry, 5 miles east of Saltville, Maccrady (T.V.A. 
218-NW) Quadrangle. 
Discussion——This species has some of the features of L. tennesseensis, to 
which it is probably related, but differs therefrom by its unusually transverse 
outline. It differs from all other species of Leptellina herein described by the 
same character. 
LEPTELLINA sp. 1 
Plate 187, B, figure 8 
A new species represented by a single brachial interior is the largest Leptel- 
lina yet found. Its length is 16.3 mm., midwidth 26.1 mm., hinge width 27.4 mm. 
plus. The brachiophores are short ; the cardinal process fused with chilidial plates 
is large and overhangs the interior; the median septum originates 24 mm. an- 
terior to the cardinal process and is narrow and elevated at the front. It termi- 
nates at the anterior end of the visceral disk which is 11 mm. long and moder- 
ately overhangs the anterior geniculated part of the valve. Muscle scars cannot 
be differentiated. 
Figured specimen.—117459. 
Horizon and locahity.—Edinburg formation (Cyrtonotella zone) in Virginia: 
In the ravine opposite the switch just east of Strasburg Junction, Strasburg 
(15’) Quadrangle. 
BILOBIA Cooper, new genus 
(Latin bi, two; lobus, lobe) 
Shells small, concavo-convex, with the pedicle valve tumid; cardinal extremi- 
ties auriculate ; anterior commissure sulcate ; surface multicostellate ; a few strong 
costellae standing out in a field of very fine costellae. 
Pedicle valve with deeply impressed large muscle field ; diductor scars elongate, 
divergent ; adductor field oval in outline, deeply impressed, separating the pos- 
terior ends of the diductors. Teeth thick; dental plates stout ; umbonal cavities 
filled by callus; dental plates extended as stout ridges around outside margin 
