362 
BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
We have not discovered the ovicell. 
It differs from Metroperiella porosa in its larger aperture, less regular tremo- 
pores and much shorter median avicularium. 
Occurrence. — Middle Jacksonian: Wilmington, North Carolina (rare); Bal- 
dock, Barnwell County, South Carolina (rare). 
Holotype. — Cat. No. 64064, U.S.N.M. 
METROPERIELLA GRANDIPORA, new species. 
Plate 47, figs. 3-6. 
Description. — The zoarium creeps over algae; it is formed of many lamellae 
superposed on the same side. The zooecia are distinct, very little elongated, 
hexagonal; the frontal is convex; the tremocyst has wide-open pores surmounting 
a very thin, finely perforated olocyst. The ovicell is large, very prominent, com- 
pletely surrounding the aperture. The aperture is large, oval, with a very wide 
rimule separated from the anter by two condyles. The median avicularium is 
salient, triangular, small and provided with very small lateral denticles. 
Measurements. — Aperture 
la= 0.15-0.16 mm. 
/m=0.45-0.16 mm. 
Zooecia 
mm* i .,.i 
Lz—0. 60-0.70 mm. 
fe=0.45-0.50 mm. 
V aviations.- — There are some wide zooecia (fig. 4) and some long zooecia 
(fig. 6), sometimes both kinds may be adjacent (fig. 3). 
Certain regular zooecia are transformed into interzooecial avicularia (fig. 6) ; 
the aperture is closed by a large spatulate mandible and articulates on two lower 
condyles. 
On the normal zooecia the condyles, on which the operculum articulates, are 
visible in the interior by turning the specimen. 
The ovicell has in front a large fragile area, which easily disappears in the 
process of fossilization (fig. 6). 
Affinities. — This species differs from Metroperiella acervata , which is also 
pleurilamellar in a larger aperture (la= 0.15 mm. instead of 0.12 mm.), the much 
smaller avicularium, its large tremopores and the absence of a salient thread around 
the zooecia. 
It differs from Metroperiella porosa in its nonbilamellar zoarium, its median 
avicularium much smaller (0. 15 mm. instead of 0.35 mm.), and in its somewhat 
larger aperture (la— 0.15 mm. instead of 0.12 mm.). 
It differs from Metroperiella albora in its wide zooecia (fe=0.45 mm. and not 
0.35 mm.), and in the absence of a wide peristome, which is white and nonsalient. 
Occurrence. — Middle Jacksonian (Castle Hayne limestone) : Wilmington, North 
Carolina (rare). 
Cotypes. — Cat. No. 64065, U.S.N.M. 
METROPERIELLA POROSA, new species 
Plate 47, figs. 7-11. 
Description. — The zoarium is free, formed of two lamellae, which are irregular, 
back to back, and separable. The zooecia are distinct, elongated, hexagonal; the 
