484 
BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 
POKELLA IRREGULARIS, new species. 
Plate 62, figs. 18-21. 
Description — The zoarium incrusts shells and brvozoa. The zooecia are dis- 
tinct, elongated and of irregular form, separated by a furrow ; the frontal is convex 
and formed of a tremocyst with numerous irregular pores. The apertura is visible 
at the base of the peristomie; the peristome is thin, oval, salient. The ovicell is 
globular, somewhat salient, little imbedded in the distal zooecia; it is hyperstomial 
and opens into the peristomie above the apertura ; it is formed of a large area very 
finely porous, surrounded by a small, very little salient collar. The oral avicu- 
larium is median, placed in the sinus of the peristome, little salient, smooth. 
Measurements . — Peristomice 
hpe= 0.06-0.08 mm. 
,lpe=0.12 mm. 
Zooecia 
\Lz= 0.55—0.65 mm. 
1/2=0.35-0.25 mm. 
V aviations . — The zooecia are quite variable in their form and in their micro- 
metric dimensions even in the zoarial regions distant from the ancestrula (figs. 
19, 20). In the interior (fig. 21) the small lyrula is visible. Figure 18' shows 
numerous traces of incompletely developed ovicells; there are some semicircular 
olocystal traces on the distal zooecia. The formation of the ovicell is therefore 
much posterior to that of the zooecia ; it probably ought to coincide with the maturity 
of the ovary, as Jolliet thought in 1877. 1 But what is the origin of the endocystal 
bud which secretes the ovicellarian olocyst ? 
Affinities . — This species differs from Porella granulosa in its polygonal tremo- 
pores and its irregular zooecia. 
It differs from Porella coronata in the absence of all adventitious avicularia. 
Occurrence . — Lower Jacksonian (Moodys marl) : Jackson, Mississippi (com- 
mon). 
Cotypes. — Cat. No. 64145, U.S.N.M. 
PORELLA GRANULOSA, new species. 
Plate 62, fig. 13. 
Description . — The zoarium incrusts brvozoa. The zooecia are distinct elon- 
gated, elliptical ; the frontal is convex, granulose, and formed by a tremocyst with 
numerous pores, separated by prominent granulations. The apertura is semilunar 
and scarcely visible exteriorly; the peristome is thin, somewhat salient, semilunar, 
deformed below by the avicularium. The ovicell is globular, little salient, some- 
what imbedded in the distal zooecia ; it is formed of a large area, very finely porous, 
surrounded by a smooth or granulose collar; it is hyperstomial and opens into the 
peristomie above the apertura. The avicularium is very little salient; it deforms, 
the peristome and opens into the peristomie. 
V 
Measurements . — Peristomice 
jhpe— 0.07 mm. 
\lpe=0.12 mm. 
Zooecia 
Ls=0A5 mm. 
fe=0.30 mm. 
1 Jolliet, Contributions a 1’ historie naturelle des cotes de Prance, Archives de Zoologie experimental et 
generale, Paris, 1877, p. 75. 
