Bulletin - United States National Museum - Smithsonian Institution

48 BULLETIN 96, UNITED STATES NATIONAL MUSEUM.
The ovicelled zooecia, different in form from the others, have a
peristomice in the form of a lunar crescent without rimule-spiramen.
The frontal is a tremocyst with tubules.
Genotype.—MetradoUum cUssimilis, new species. Jacksonian.
METRADOLIUM DISSIMILIS, new species.
Plate 4, tig. 10.
Description.—The zoarium is free, bilamellar, branching; the
fronds are wide, thick, distorted or undulated, dichotomous. The
zocecia are distinct, elongated, elliptical. The frontal is a tremocyst
with tubules resting on an olocyst with very small pores correspond-
ing to the tubules. The peristomie is deep and very oblique ; the aper-
tura is small and suborbicular ; the peristomice is orbicular ; the spiramen
is median, more or less distant from the peristomice. There are
two oral avicularia symmetrically placed but dissimilar in form and
size ; the smaller is round, simple, nonsalient ; the larger is enormous,
oval, salient, with pivot. The ovicell is enormous, buried in the distal
zocecia, hyperstomial but opening largely into the peristomie ;
salient
and globular; its peristomice has the form of a lunar crescent; the
ovicelled zooecia bear only a small avicularium with pivot.
. \Jipe=0.U-0.1^ mm.
Measurements.—PevistomicQ (exterior) W^^g—o i5_o.20 mm.
|Z2=0.74-0.7G mm.
Zooecia (exterior) j^;,= 0.40-0.50 mm.
Occurrence.—Middle Jacksonian: Wilmington, North Carolina
(very common), and various localities in South Carolina and Georgia.
Type.—OAi. No. 62596, U.S.N.M.
LEIOSELLA, new genus.
{Leios, smooth, having reference to the nature of the frontal.)
The frontal is an olocyst. The peristomice of the ovicelled zooecia-
is of different form from that of the other zooecia ;
cent and deprived of rimule-spiramen.
it is a lunar cres-
Genotype.—Leiosella rostrifera.^ new species. Vicksburgian.
This genus differs from Metradolium only in the nature of the
frontal, which is here a very thick olocyst.
LEIOSELLA ROSTRIFERA, new species.
Plate 5, fig. 1.
Description.—T\\e zoarium is free, bilamellar; the fronds are nar-
row, flat, claviform, bifurcated. The zooecia are elongated, distinct,
ovoid ; the frontal is smooth, convex, formed by a thick olocyst. The
peristomice is irregular; the rimule-spiramen is bordered laterally