Fauna of the Morrow Group 
139 
apertures in a 5 mm. space along the ranges, interspaces equal 
to about IV 2 the diameter of the apertures but between aper- 
tures in adjacent rows the interspace is usually less than a 
diameter. 
Horizon and locality. Brentwood limestone: near Fayette- 
ville, Arkansas (Station 185). Kessler limestone: East Moun- 
tain, Fayetteville, Arkansas (Station 209) . Morrow formation : 
near Choteau, Oklahoma (Station 302). 
Coscinium gracilens n. sp. 
Plate y//, figure U. 
Description. Zoarium a bifoliate expansion pierced by oval 
or circular fenestrules regularly arranged in quincunx. Spaces 
between the fenestrules comparatively small, the openings 
being separated by distances of about 2.5 mm. while the 
fenestrules average 2.1 mm, in diameter, varying from elongate 
oval in shape with dimensions of 2.3 by 1.6 mm., to circular 
in shape with diameters of 2.0 to 2.2 mm. Zooecia irregularly 
scattered over the surfaces of the fronds with a narrow non- 
poriferous strip around each fenestrule; an indefinite sugges- 
tion of a linear arrangement of the apertures may be observed 
in some portions of the frond with five or six of the irregular 
rows occurring between each two adjacent fenestrules. The 
apertures are not well preserved in the material at hand but 
they seem to have had an unequally elevated peristome and a 
lunarium directed away from the nearest fenestrule; apertures 
average 0.1 mm. in diameter and are separated by interspaces 
of more than their diameters. 
Remarks. This species is apparently less abundant than the 
foregoing one in the Morrow formations and is characterized 
by the very slender inosculating branches which make up the 
frond and by the small number of zooecial ranges present in 
those parts of the zoarium where a linear development of the 
apertures is noticeable. 
Horizon and locality. Brentwood limestone: near Fayette- 
ville, Arkansas (Station 134). Morrow formation: near Cho- 
teau, Oklahoma (Station 302). 
