NORTH AMERICAN EARLY TERTIARY BRYOZOA. 
489 
Finally, the avicularian zooecia are rather frequent; they are characterized 
by a very large opening, narrowed in its median part. We know that the operculum 
is replaced there by a mandible and that the polypide has disappeared by histolysis. 
Occurrence. — Middle Jacksonian (Castle Hayne limestone) : Wilmington, North 
Carolina (rare) ; near Lenucls Ferry, South Carolina (rare). 
Holotype. — Cat. No. 64152, U.S.N.M. 
PORELLA ABDITA, new species. 
Plate 65, figs. 1-3. 
Description.— The zoarium is large, bilamellar, and formed of two lamellae, 
back to back, and inseparable. The zooecia are indistinct; the frontal is convex 
and formed of a tremocyst with irregular pores. The peristomice is orbicular or 
elliptical. The median avicularium is very small, buried in the thickness of the 
tremocyst, opening in the peristomie, hardly visible exteriorly. Often a small 
adventitious avicularium is placed in the vicinity of the peristomice. 
Measurements. — Peristomice \^ e 0.20 mm. 
\lpe= 0.15 mm. 
Zooecia 
(Ls= 0.70-0.75 mm. 
\lz= 0.30-0.35 mm. 
Affinities. — We have collected only a small number of specimens and it is 
possible, therefore, that they are related to another species of which they may be 
the strongly calcified representatives. This is, in fact, the habitual variation in 
Porella denticulifera and Porella jacksonica. To be certain of the identification 
with the latter species it will be necessary to find a greater number of specimens 
in the same localities. 
Occurrence. — Upper Jacksonian (Ocala limestone) : Alachua, Florida (rare) ; 
9 miles north of Ocala, Florida (rare). 
Cotypes. — Cat. Nos. 64154, 64155, U.S.N.M. 
PORELLA PORTENTOSA, new species. 
Plate 64, figs. 10-23. 
Description. — The zoarium is bilamellar; the fronds are flat or a little un- 
dulated. The zooecia are distinct, quite elongated, tubular; the frontal is convex 
and formed of a tremocyst with large tubular pores, supported by a very thin, 
perforated olocyst; the tubules have thick walls and are separated from one 
another. The apertura is semilunar, with the proximal border convex; the peri- 
stome is very thin, hardly salient. The ovicell is much embedded in the distal 
zooecium, hardly prominent ; its frontal is a perforated area ; the ovicell is hyper- 
stomial and opens into the peristomie. The avicularium is placed entirely within 
the peristomie. 
Measurements. — Peristomice ( mm ‘ Zooecia { f ~ ^ mm ’ 
[lpe= 0.12 mm. Us=0.26mm. 
Variations. — This species is quite remarkable. The tubules are not adjacent 
and are separated from each other; this results in the frontal having a fantastic 
aspect which is impossible to describe. When these tubules are adjacent (figs. 11, 
