NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
363 
frontal is little convex and formed by a tremocyst with numerous wide open pores. 
The aperture is oval, with a wide, rounded rimule, separated from the anter by 
two condyles visible in the interior. The ovicell is large, globular, salient; it 
completely surrounds the aperture, forming around it a prominent peristomie; 
it is formed of a large frontal area surrounded by a salient collar. The median 
avicularium is long, very thin, remote from the aperture. 
Measurements. — Aperture 
| ha= 0.12-0.14 mm. 
[7^=0.12-0.14 mm. 
Zooecia 
f Lz= 0.60-0.70 mm 
172=0.50 mm. 
Variations. — The beak of the avicularium is very long, thin, and fragile; it 
is only visible on the best preserved specimens (fig. 11) ; on others it has the aspect 
of a small triangular pore (fig. 8), but always remote from the aperture and not 
salient. 
The zooecia with a thick tremocyst are sometimes bordered by a small salient 
thread (fig. 8). 
The frontal area of the ovicell is fragile; it often disappears in the process of 
fossilization. 
The orifice of the ovicelled zooecia is quite variable. The operation of the 
operculum appears to be complex. It must be lowered much externally to permit 
the extrusion of the tentacles, which ought, moreover, to be very thin. The oper- 
culum never closes the ovicell because the outer orifice does not exactly correspond 
to its form, but in opening it offer a shelter sufficient for the passage of the eggs. 
It is probable also, as in many other Schizoporellae that it remains closed during 
the escape of the larvae. 
In figure 8 the reader may note two zooecia which are transformed into inter- 
zooecial avicularia analogous to the zooecia of Arthropoma cecilii Savigny-Audouin, 
1812-1826, figured in 1890 by Kirkpatrick and which we have reproduced on text 
figure 105. 
We have observed (fig. 8) a calcified zooecium whose aperture is covered by 
the tremocyst. 
The median avicularium is the result of the development of an inner bud, 
as it is easy to note on inner surfaces. 
Affinities.— This species differs from Metroperiella biplan at a, in which zoarium 
is also bilamellar, in its much larger instead of very minute tremopores. 
It differs from M eiroperiella grandipora in its smaller aperture (la = 0.12 mm. 
instead of 0.15 mm), its median avicularium, which is very large and remote from 
the aperture, and its zoarium, which is bilamellar and not pleurilamellar. 
Occurrence. — Middle Jacksonian: Near Lenuds Ferry, South Carolina (com- 
mon) ; Wilmington, North Carolina (common) ; 3£ miles south of Perry, Georgia 
(rare). 
Cotypes. — Cat. No. 64066, U.S.N.M. 
