124 
Kirtley F. Mather 
Polypora reversispina n. sp. 
Plate V, figures U, ^-a. 
Description. Zoarium a funnel-shaped, reticulated expansion 
composed of bifurcating branches united at regular intervals by 
short dissepiments, with the zooecial apertures on the inner face. 
Branches broadly convex and flexuous on the obverse, sub-cari- 
nate and more rigid on the reverse face; 0.8 to 1.0 mm. in width 
on the poriferous, 0.3 to 0.4 mm. wide on the non-poriferous side; 
9 to 10 occurring in the space of 1 cm. ; ornamented on the reverse 
by numerous small, hollow, rounded spines or tubercles irregu- 
larly situated but commonly with three or four to a fenestrule. 
Fenestrule sub-quadrate or sub-hexagonal on the reverse, oval 
and much smaller on the obverse, 6 or 7 in a centimeter longi- 
tudinally, 1.0 to 1.2 by 0.7 to 0.8 mm. on the reverse face and 
0.3 by 0.4 mm. on the obverse. Dissepiments short, as wide as 
or wider than the branches; convex or somewhat flattened, on 
a level with or slightly depressed below the surface of the zoa- 
rium on the non-poriferous side; shorter and broader toward 
the obverse face with but a narrow strip of non-poriferous sub- 
stance remaining between the almost anastomosing branches and 
in some instances even this disappearing so that the fenestrules 
are completely surrounded by apertures. Zooecial apertures 
arranged in 4 or 5, or in places 6 alternating ranges which are 
distinctly sinuous; apertures small, circular, a diameter and a 
half apart longitudinally and less than a diameter apart obliquely, 
about 21 in 5 mm. 
Remarks. Like P. transiers of the Salt Range, P. reversispina 
may be considered as transitional between the genera Polypora 
and Phyllopora. It is placed with the former because of its 
reticulated appearance with distinct dissepiments, as viewed from 
the reverse side, and because the zooecial apertures are situated 
on the inside rather than the outside of the ‘"funnel” although 
on its poriferous side it must resemble Phyllopora more than 
Polypora, 
Horizon and locality. Hale formation: East Mountain, Fay- 
etteville, Arkansas (Station 136). 
