488 
BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
PORELLA UNGUICULATA, new species. 
Plate 64, figs. 1-5. 
Description. — The zoarium is unilamellar and creeps on algae. The zooecia 
are distinct, elongated, fusiform ; the frontal is convex and is terminated distally by 
a long ungulate mucro covering the apertura; it is formed of a tremocyst with 
scattered pores, disposed in quincunx. The apertura is invisible exteriorly; the 
peristome is wanting. The ovicell is hardly salient; the pores of the area are much 
smaller than those of the frontal; it is hyperstomial and opens into the peristomie. 
The median avicularium is large, oblique, smooth, totally burying the apertura. 
M easurements. — Zooecia 
\Lz= 0.72 mm. 
tfe—0.37 mm. 
Affinities. — This species much resembles Porella jachsonica , of which it is per- 
haps the creeping form. It differs from it in its smaller tremopores, the exagger- 
ated length of its median avicularium, which always covers the apertura on the 
well preserved specimens, and in the absence of all adventitious avicularia. 
In the interior (fig. 5) the olocyst is thick; the proximal border of the apertura 
is convex; the mucro is visible. 
On the zoarial margins the avicularium is more fragile atid more easily broken 
(fig. 3). 
Occurrence. — Middle Jacksonian (Castle Hayne limestone) : Wilmington, North 
Carolina (common). 
Cotypes. — Cat. No. 64151, U.S.N.M. 
PORELLA PLANULATA, new species. 
Plate 64, figs. 6-9. 
Description. — The zoarium is bilamellar and formed of two lamellae, back to 
back and inseparable. The zooecia are distinct, elongated, rounded in front, nar- 
rowed behind, separated by a salient thread; the frontal is -flat and formed of a 
tremocyst with large tubules resting on an olocyst with small pores. The apertura 
(in the interior) is formed of a semilunar anter and of a very concave poster; at 
the exterior the peristomice is elliptical and the peristome very thin. The median 
avicularium is very small, buried in the thickness of the tremocyst and opens into 
the peristomie; it is visible only by abrasion of the surface. Sometimes avicularian 
zooecia are intercalated among the normal zooecia. 
Measurements. — Peristomice mm ’ 
[^6=0.18 mm. 
Zooecia 
J,Cs=0.90-1.10 mm. 
[lz= 0.40-0.45 mm. 
Affinities.- — This grand and beautiful species is remarkable, but we still possess 
no specimen with an ovicell. The median avicularium is absolutely invisible ex- 
teriorly ; by properly inclining the preparation its orifice is visible ; upon abrasion 
of the surface it appears like a small cavity in the thickness of the tremocyst (fig. 9). 
In the interior certain zooecia are divided in two parts by a partition, of 
whose use we are absolutely ignorant (fig. 8). 
