118 
Kirtley F. Mather 
commonly in three ranges ; apertures are circular and nearly two 
diameters apart in the rows. A fragment of a similar form 
from a second locality displays numerous small spines or nodes 
in rows between the zooecia as in the type material. 
Horizon and locality, Brentwood limestone: near Fayette- 
ville, Arkansas (Station 135). Morrow formation: near Ft. 
Gibson, Oklahoma (Station 301). 
Polypora purduei n. sp. 
Plate IV, figures 13-1 4-. 
Description, Zoarium a foliar, fan-shaped expansion, 2 or 3 
cm. in height and somewhat undulating. Branches rigid, bifur- 
cating at irregular intervals, 8 to 11 occurring in a space of 
1 cm. ; averaging 0.5 mm. in width but increasing to 0.7 or 0.8 
mm. just before a bifurcation and decreasing to half that width 
immediately thereafter ; convex and striated on reverse and con- 
vex to somewhat flattened on obverse face. Dissepiments some- 
what depressed on either face, of nearly the same thickness from 
branch to branch as observed on the reverse side but increasing 
in width terminally as seen from the obverse face, averaging 
0.35 mm. in width but in some instances only 0.2 mm., or again 
as great as 0.45 mm. Fenestrules about twice as long as wide, 
subquadrate on the reverse and sub-oval on the obverse face, 
6 or 7 to the centimeter longitudinally, and varying in length 
from 0.8 to 1.1 mm. Zooecia arranged in four or flve rows 
increasing to six or seven before and decreasing to three after 
bifurcation, 20 or 21 occurring in a space of 5 mm. ; the apertures 
circular, separated by about twice their diameter in the rows; 
very faint, sinuous, rounded ridges separate the ranges as ob- 
served on unweathered surfaces and in places a slight elevation 
suggestive of a node may develop along the ridges near the 
middle of the branch. 
Remarks, This species falls into a group of mid-Carbonifer- 
ous Polyporas which are closely alike in characteristics and pre- 
sumably intergrade rather freely one to the other. It may be 
distinguished from P, bassleri by the absence of the small spines 
on the poriferous side of the branches and by the smaller number 
of fenestrules to the centimeter resulting from the slightly 
greater width of the dissepiments. From P, cestriensis it is dis- 
