114 
Kirtley F. Mather 
Horizon and locality. Brentwood limestone : Fayetteville 
(Station 148), and Baxter Mountain (Station 153), Arkansas. 
Morrow formation: near Ft. Gibson (Stations 296 and 301), 
and Choteau (Station 306), Oklahoma. 
Fenestella venusta n. sp. 
Plate IV, figures 9-1 Oa. 
Description. Zoarium an undulatory foliar expansion prob- 
ably not over 2.5 cm. in length or breadth, composed of slender 
branches exceedingly closely spaced and united by short dissepi- 
ments at regular and frequent intervals. Branches bifurcating 
at irregular intervals; moderately rigid; rounded and longitu- 
dinally striated on the reverse, bearing a carinate median keel 
on the obverse; from 32 to 38, commonly about 36, in 10 mm. 
Dissepiments about two-thirds as wide as the branches, broad- 
ening at either end ; very slightly depressed on the obverse, more 
strongly depressed on the reverse face. Fenestrules elongate 
oval in outline, slightly more elongate on the obverse than on 
the reverse face; very constantly 32 in 10 mm. longitudinally. 
Zooecia in two alternating rows generally arranged so that one 
occurs at the union of each dissepiment with the branch and one 
midway between the dissepiments ; ranges separated by a slightly 
flexuous, carinate ridge bearing small nodes irregularly situated 
along its crest. Apertures circular, about 1 diameter apart in 
the rows, with about 32 or 33 occurring in the space of 5 mm. 
Remarks. This very delicate form may be readily distin- 
guished from previously described members of the genus by its 
closely spaced branches and small fenestrules. In the number 
of branches and fenestrules in a centimeter it very appreciably 
exceeds F. tenax, the most finely '‘woven” of the Mississippian 
species of Fenestella. From that form it may also be distin- 
guished by its comparatively more robust dissepiments. 
Horizon and locality. Hale formation: East Mountain, Fay- 
etteville, Arkansas (Station 136). Brentwood limestone: near 
Brentwood (Station 145), and Fayetteville (Station 135) , Arkan- 
sas. Kessler limestone: near Brentwood, Arkansas (Station 
144). Morrow formation: near Ft. Gibson, Oklahoma (Station 
301). 
