128 
Kirtley F. Mather 
ACANTHOCLADIID^ 
Genus SEPTOPORA Prout 
Septopora reversispina n. sp. 
Plate VI, figures 2, 2a. 
Description. Zoarium an undulating foliar expansion com- 
posed of rigid branches united at regular intervals by slender 
poriferous dissepiments into a compact network. Branches 
increase in number by interpolation with 10 occurring in each 
centimeter transversely ; on the reverse they are narrowly 
rounded, 0.2 to 0.4 mm. in width, and ornamented by round, more 
or less pointed spines projecting slightly downward and generally 
situated opposite each junction with a dissepiment; on the 
obverse the branches are somewhat broader. Dissepiments 
rounded, more slender than the branches and depressed below 
them, arched across the space between the branches and expanded 
^terminally. Fenestrules subquadrate on the reverse, 10 to the 
centimeter, 0.6 to 0.8 mm. long and 0.4 to 0.7 mm. wide, more 
oval and smaller on the obverse. Zooecia in 2 ranges along the 
branches, about 25 occurring in the space of 5 mm., 5 or 6 on 
each dissepiment; accessory pores on the reverse face small, 
about 0.04 mm. in diameter, usually one or two situated near 
either end of each dissepiment. 
Remarks. Distinguishing features of this species are the 
equality in the number of branches and fenestrules in a unit dis- 
tance, the increase in the number of branches by interpolation, 
and the presence of spines on the reverse face of the frond. 
None of the previously described members of the genus appear 
to be closely comparable to it. 
Horizon and locality. Brentwood limestone : near Brentwood, 
Arkansas (Station 145). 
Septopora crebripora n. sp. 
Plate VI, figures 1, la. 
Description. Zoarium a compact, foliar, fan-shaped network [ 
composed of bifurcating branches united at regular intervals by j 
poriferous dissepiments. Branches rigid, 10 or 12 to the centi- 
meter, 0.3 to 0.4 mm. in width on the reverse, increasing to 0.6 
or 0.7 mm. before bifurcation and as narrow as 0.2 mm. for short ; 
