116 
Kirtley F, Mather 
of zooecia, representing that portion of the fenestrated expansion 
which is enclosed in the solid axis, are very moderately convex 
upward and meet in the center at an obtuse angle, about 115\ 
Remarks. Among the Mississippian Archimedes only one, A. 
swallovanus, displays a close resemblance to A. juvenis and from 
it the latter may be distinguished by the somewhat wider spacing 
of the volutions and the shape of the flanges which in the older 
forms are directed distinctly, though moderately, upward. The 
slight convexity of the lines of zooecia, seen in longitudinal sec- 
tion as mentioned above, seems also to be quite uncommon in 
an axis with so widely spaced volutions. 
Horizon and locality. Brentwood limestone : Baxter Mountain 
and Fayetteville, Arkansas (Stations 153 and 148). 
Genus POLYPORA MacCoy 
Polypora triseriata n. sp. 
Plate V, -figures 2-3. 
Description. Zoarium a foliar, fan-shaped, undulating expan- 
sion probably not over 4 cm. in height, composed of delicate, 
rounded, bifurcating branches united at regular intervals by 
somewhat depressed, rounded dissepiments whose diameter is 
about two-thirds that of the branches. Branches averaging 19 
in 1 cm., but with as few as 17 or as many as 22 in places ; about 
0.4 mm. in width, expanding to a width of 0.6 mm. or even more 
at bifurcations ; flnely striated on the reverse side and somewhat 
flattened on the aperture-bearing surface. Fenestrules more or 
less oval, varying but little from 0.4 mm. in length but the width 
varying from 0.2 mm. to nearly as great as the length ; 14 to 16 
in 1 cm. longitudinally. Apertures circular, arranged in two, 
three, or four rows, almost invariably alternating, each row sep- 
arated from adjacent rows by a faint, not noticeably nodiferous, 
sinuous ridge or keel ; along any branch the three-rowed arrange- 
ment of the apertures is the normal manner with the median 
row prominently displayed along the flattened surface of the 
branch and the lateral rows partially concealed along its sides 
but for a distance of one or two, or even four millimeters imme- 
diately before a bifurcation, the additional row is added and 
over a similar space, after bifurcation has occurred, only two 
rows are present and the resemblance to Fenestella is strong; 
