PART I CHAZYAN AND RELATED BRACHIOPODS—COOPER 725 
the cardinal process. The median septa extend nearly but not quite into the 
cavity. 
SOWERBYITES DELICATUS Cooper, new species 
Plate 179, B, figures 7-20 
Shell of about medium size for the genus, wider than long, length about two- 
thirds the width; cardinal extremities approximately a right angle and slightly 
auriculate; sides gently convex; anterior margin broadly rounded; ornamenta- 
tion as in other species but very fine; about 10 of the larger costellae occupy 
5 mm. at the front margin. Lamellae poorly preserved, observed mostly near the 
front margin. 
Pedicle valve moderately convex in lateral profile and with the maximum con- 
vexity slightly anterior to the middle ; anterior profile broadly convex and slightly 
humped in the median region; umbo narrowly swollen to form a low fold that 
extends more or less distinctly to the middle or slightly beyond; median region 
swollen ; flanks gently convex and with long, gentle slopes to the margins; an- 
terior slope moderately long and moderately steep. Interarea long, apsacline. 
Brachial valve concave, with the maximum concavity just anterior to the cen- 
ter; umbo concave, the concavity extending nearly to the middle as a shallow 
and narrow sulcus; flanks gently concave; interarea short, hypercline. 
Interior of pedicle valve with moderately strong callosities at the anterior ends 
of the diductor scars; pallial marks not pronounced. Interior of brachial valve 
with small and short brachial processes; median septum strongly elevated and 
thickened at the front; outside pair of lateral septa poorly developed. 
Measurements in mm.— Brachial Hinge 
Length length Midwidth width Thickness 
EVOLObY PEM arsitrere blelovsiel sieie «esdiete ole 10.9 9.8 14.2 14.2 1.9 
Paratype, (117300d.). a. aes 5.01 9.9 88 14.7 16.2 E7 
Types.—Holotype: 117399e; figured paratypes: 117399a-d,f-h. 
Horizon and locality.—Low in the Sevier shale in Tennessee: 1.8 miles S. 18° 
E. of Athens, Athens (T.V.A. 125-NE) Quadrangle. 
Discussion.—This species has been found only at a single locality where it oc- 
curs in countless numbers in a calcareous sandstone that forms a reeflike mass. 
Sowerbyites delicatus is characterized by its small size, moderately auriculate 
cardinal extremities, gentle convexity of the pedicle valve, and gentle concavity 
in the brachial valve. The species in unlike S. triseptatus in its small size and 
relatively elongate form, and its cardinal extremities are not so strongly alate. It 
is smaller than all the other described species except S. hami. It is larger than 
the latter form but is not so convex in the pedicle valve nor so concave in the 
brachial valve. 
SOWERBYITES GILDERSLEEVEI Cooper, new species 
Plate 183, A, figures 1-16 
Shell large, semicircular in outline with slightly obtuse to acutely angular car- 
dinal extremities. Anterior margin very broadly rounded to nearly straight. 
