Fauna of the Morrow Group 
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tinguished by its smaller and less elongated fenestrules, its 
stouter dissepiments and broader branches, and the somewhat 
closer spacing of the zooecial apertures. In comparison with 
P. corticosa the absence of the zooecial filling near the base of 
the zoarium, the proportionately narrower fenestrules, and the 
broader branches may be noted. Comparing P. purduei with P. 
fastuosa, a distinguishing characteristic is the lesser prominence 
of the dissepiments, which in the latter species are carinate and 
as high as the branches as well as less than a third their width. 
From P. ulrichi this species is distinguished by the closer spacing 
of zooecial apertures, the less elongated fenestrules, and the 
absence of nodes on the reverse face. 
It is noteworthy that each of these five species is recorded 
from the Coal Measures except P. corticosa, a Chester form with 
which P. cestriensis also occurs, so that the form under discus- 
sion is in a sense transitional between the Chester and Coal 
Measures types with its affinities closer to the latter than to 
the former. 
Horizon and locality. Hale formation: East Mountain, Fay- 
etteville, Arkansas (Station 136). Brentwood limestone: near 
Fayetteville, Arkansas (Station 135) ; Sawney Hollow, Oklahoma 
(Station 210) . Morrow formation : vicinity of Ft. Gibson, Okla- 
homa (Stations 301 and 303). 
Polypora washingtonensis n. sp. 
Plate IV, figures 15, 15a. 
Description. Zoarium a foliar, fan-shaped expansion, 2 or 3 
cm. in height, undulating or regularly curved transversely, with 
the apertures on the inside. Branches strong, rigid as observed 
from the obverse and slightly flexuous as seen from the reverse 
side, sub-triangular in cross-section; 0.1 or 0.2 mm. in width 
on the reverse face of the zoarium and 0.7 or 0.8 mm., or even 
1.0 mm. below bifurcations, in width on the poriferous side ; 8 to 
10, usually 9 to the centimeter. Dissepiments sub-carinate, with 
cross-section similar to that of the branches; slightly depressed 
below either face; 0.1 mm. wide near the reverse face and 0.6 
or 0.7 mm. wide near the obverse face where they are much wider 
at the ends than midway between the branches. Fenestrules 
sub-quadrate as viewed from the non-poriferous side, very reg- 
