Fauna of the Morrow Group 
137 
but distinct longitudinal costae, with a variable number of zooe- 
cia, normally arranged in curving linear series, upon the pinnate 
projections; apertures subcircular; small, 11 or 12 occurring in 
5 mm. along the longitudinal ranges, peristomes faint. 
Remarks. The large size of the branches and their sinuous 
margins sharply distinguish this species from the other mem- 
bers of the genus. It is not closely comparable to any of the 
previously known Carboniferous forms. 
Horizon and locality. Hale formation: East Mountain, Fay- 
etteville, Arkansas (Station 136). Brentwood limestone, near 
Fayetteville, Arkansas (Station 135). 
Cystodictya flexuosa n. sp. 
Plate VII, figures 8-9a. 
Description. Zoarium consisting of ramose, bifoliate, flexu- 
ous branches with an elongate elliptical cross-section. Branches 
are from 2.0 to 2.5 mm. in width and divide laterally at intervals 
of 3 to 5 mm. ; margins modified by short rounding protuber- 
ances occurring at irregular distances which, when present on 
both margins opposite each other, increase the width of the 
branch to 3.0 mm. or even more. Zooecia arranged in indefinite 
longitudinal and oblique series, with seven or eight of the for- 
mer on each face of the zoarium; five or six apertures are 
clustered upon the lateral protuberances when they are present; 
the non-poriferous marginal portion of the branches very nar- 
row. No longitudinal ridges are observable but in some instances 
an indefinite oblique furrow is present between the apertures, 
especially when the oblique serial arrangement is more perfect. 
Apertures oval or circular, 11 or 12 in 5 mm. longitudinally, 
oblique and with strongly elevated, rather thin peristomes when 
the preservation is good ; appearing more nearly perpendicular 
to surface and with less elevated but thicker peristomes when 
somewhat worn. 
Remarks. C. zigzag from the Keokuk limestone is probably 
somewhat closely related to this species. The Morrow form is 
distinguished from the earlier one by the generally more robust 
branches and the more closely spaced apertures as well as the 
tendency toward an arrangement of the zooecia in oblique series. 
Horizon and locality. Morrow formation: near Ft. Gibson, 
Oklahoma (Stations 296 and 301). 
