286 
BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
MEMBRANIPORELLA CRASSICOLLIS, new species. 
Plate 4, figs. 24, 25. 
Description.— The zoarium is bilamellar and free. The zooecia are little dis- 
tinct, being confluent by their mural rims, elongated, fusiform ; the area is cribri- 
form, contains three to five pairs of transversal slits, and is deep and flat. The 
aperture is suborbicular, somewhat transverse, and is surrounded by a thick, promi- 
nent peristome. The ovicell is small, salient, convex, smooth; it is always closed 
by the operculum. There is often a large, simple, round avicularium placed on the 
mural rim to the right or the left. 
Measurements. — Aperture 
ha— 0.12 mm. 
7a=0.15 mm. 
Zooecium 
( 7.?= 0.85 mm. 
1. As =0.70 mm. 
Affinities. — The prominence of its peristome characterizes this species. It 
differs from M emit) ran ip or ell a planula in its costules, which are not flat, and in 
the zooecial mural rims, which are joined to one another. 
From MembraniporeZla bioculata it may be distinguished by its less numerous 
slits and by the entire absence of an oral mucro. 
O commence. — Midwayan: One mile west of Fort Gaines, Georgia (rare); 
Mabelvale, near Little Rock, Arkansas (rare). 
Cotypes. — Cat. No. 63806, U.S.N.M. 
MEMBRANIPORELLA PLANULA, new species. 
Plate 5, figs. 8-10. 
Description.— The zoarium is free and bilamellar. The zooecia are distinct, 
separated by a furrow, elongated, fusiform, bordered by a thin mural rim; the 
cribriform area is of little depth, formed of flat costules, and contains five or six 
pairs of transverse slits. The aperture is semilunar. The two small oral avicularia 
are symmetrically placed on the distal part of the mural rim; the pivot is indicated 
by two lateral denticles. 
Measurem en ts. — Aperture 
7/a=0.10-0.12 mm. 
la= 0.12 mm. 
Zooecia 
f 7,0=0.85 mm. 
1 7s=0.36 mm. 
Affinities:— The micrometrical measurements are rather variable. Those given 
above correspond to figure 9, but in figure 8 the zooecia are smaller. In the interior 
(fig. 10) the measurements are from 0.95 to 1.10 mm. for the length and from 
0.30 to 0.35 mm. for the width. 
This species differs from M embraniporelia crassicoTlis in its more numerous, 
flat costules, in the absence of a prominent peristome, and in its zooecia, which 
are separated by a deep furrow. 
Compared with M embraniporella ulnchi it may be distinguished by its much 
smaller and less constant oral avicularia ( Lv 0.15 mm. and not 0.25 mm.) and by 
the much larger slits of the cribriform area (0.05 mm. and not 0.01 mm.). 
Occunmnce. — Midwayan (Clayton limestone) : Mabelvale, near Little Rock, 
Arkansas (rare); Luverne, Crenshaw County, Alabama (rare). 
Cotypes. — Cat. Nos. 63808, 63809, U.S.N.M. 
