186 
Kirtley F. Mather 
stone: East Mountain, Fayetteville, Arkansas (Station ?209). 
Morrow formation: near Gore, Oklahoma (Stations 304 and 
305). 
Spirifer goreii n. sp. 
Plate XII, figures 10-1 la. 
Description. Shell large, width twice as great as length, 
greatest width along hinge-line, valves moderately convex. The 
dimensions of an average individual, in part estimated, are: 
length from umbonal region of pedicle valve to anterior margin, 
21 mm. ; length of hinge-line, 53 mm. ; thickness of shell, 15 mm. 
Pedicle valve moderately and regularly convex longitudinally, 
the transverse curvature of surface concave upwards on either 
side of the sinus due to the elevation of the middle part of the 
shell above the flattened lateral extremities ; beak comparatively 
slender, strongly elevated above cardinal line and incurved over 
the delthyrium; umbonal region not projecting far beyond tiie 
cardinal area; cardinal area about one-tenth as high as long, 
gently concave, transversely striated, the cardinal margin flnely 
orenulate; delthyrium a large isosceles triangle; mesial sinus 
originating as a simple depression on the beak, well-deflned and 
bearing two or three plications on the umbo, less well-deflned 
and with more numerous plications anteriorly; lateral slopes 
of valve bearing from 15 to 20 rounded, rarely bifurcating plica- 
tions which are strongest adjacent to the mesial sinus and grow 
fainter toward the cardinal extremities where they may be i 
entirely obsolete. 
Brachial valve more shallow than pedicle, gently convex longi- | 
tudinally, the transverse curvature slightly concave upward on 
either side of the mesial fold as in the opposite valve ; beak incon- 
spicuous, cardinal area very low, umbonal region somewhat ; 
strongly elevated above lateral extremities but not projected 
beyond cardinal line; mesial fold originating on the umbo as a 
single plication but becoming stronger, though not well-defined, [ 
as it expands anteriorly, the plications bifurcating until near the 
margin there may be 8 or 10 ; plications of lateral surfaces as 
on the pedicle valve. 
The minute surface markings consist of fine radiating striae, 
stronger between the plications than on their crests, crossed by i 
equally fine, wavy, concentric lines of growth. 
