180 
Kirtley F. Mather 
emargination resulting from the produced sinus of the pedicle 
valve. 
Surface markings consisting of a few irregularly scattered, 
rounded, growth lines which are about as numerous in the um- 
bonal region as near the margin. Shell structure finely punctate. 
Remarks. Although there is not sufficient material represent- 
ing this species, only four specimens having come to hand, to 
permit of determining the internal characters by grinding, it 
is evident that the form is a Dielasma. In one specimen the 
shell is sufficiently translucent to show the position of the internal 
lamellae of the brachial valve which present the arrangement 
of the genus. 
Ho rizon and locality. Brentwood limestone: near Fayette- 
ville, Arkansas (Stations 134 and 135). 
Dielasma arkansanum Weller 
Plate XI, figures 12-12h. 
1914. Dielasma arkansanum. Weller, 111. State Geol. Surv., Mon. I, 
p. 269, pi. 31, figs. 35-44. 
Washington County, Arkansas; Webb City, Missouri. 
(Carterville formation?) 
Associated with D. suhsyatulatum at two localities were found 
a few specimens of the form which has been described by Dr. 
Weller as D. arkansanum. This species is an abundant one in 
the Fayetteville shale and the type material was probably de- 
rived from that formation. It is comparatively rare in the Mor- 
row group. No differences are observable between the indi- 
viduals from the two horizons. 
Horizon and locality. Brentwood limestone: near Fayette- 
ville, Arkansas (Stations 134 and 135). 
Genus GIRTYELLA Weller 
Girtyella? emarginata n. sp. 
Plate XI, figures IS-lSb. 
Description. Shell small, terebratuliform, anterior margin 
concave, valves strongly convex, greatest width a little in front 
of the middle. The dimensions of one of the cotypes are : length, 
7.0 mm. ; width, 6.0 mm. ; thickness, 4.2 mm. 
Pedicle valve somewhat gibbose, strongly and regularly con- 
vex from beak to anterior margin, the slope from the middle of 
