Bulletin - United States National Museum - Smithsonian Institution

22 BULLETIN 9G, UNITED STATES NATIONAL MUSEUM.
Genotype.—Stamenocella mediaviculifera^ new species.
Range.—Senonian-Viclcsbiirgiun.
The genus which is nearest to this type of structure is Bactrellaria
Marsson, 1887, in which the zooecia are identical, but are disposed on
a single side of a triserial zoarium. The two genera undoubtedly
belong to the same family.
STAMENOCELLA MEDIAVICULIFERA, new species.
Plate 3, fig. 1.
Description.—The zoarium is bilamellar, Avith the two lamellae
back to back and inseparable. The zoa3cia are very elongated, narrowed
behind, distinct or indistinct; the mural rim is thin, salient,
somewhat enlarged and attenuated, rounded, smooth. The opesium
is elliptical or oval, entire; the gymnocyst is somewhat convex and
nearly as long as the opesium. The avicularium is salient and ])laced
in the middle of the gymnocyst. The ovicell is rarely intact.
Measurements.—Opesia
Zocecia
A6>=0.40 nun.
Zo=0.1G mm.
fZs=0.80 mm.
Zs=: 0.20-0.24 mm.
Variations and affinities.—This species apparently lived in agitated
waters. Although widely distributed, it is often very rare, and
specimens are always more or less worn. In this condition the mural
rim is worn away and invisible, the zooecia indistinct, and the avi-
cularia absent or replaced by a concave cicatrix. We have never
found the ovicell intact ; it is always more or less broken but its place
is clearly visible on the gymnocyst. The avicularium is of the sim-
13le type without denticles or pivot.
Occurrence.—Middle Jacksonian: Rich Hill, Crawford County,
and other localities in Georgia (very common).
Type.—Q^'^i. No. G2581, U.S.N.M.
Family AETEIDAE Smitt, 1867..
Zoarium composed of creeping branches more or less adherent to
the substratum, often growing in free tufts adherent only part of
their length. Zooecia uniserial, arising from each other in a tubular
prolongation of greater or less length. Opesium terminal, opercular
valve at its summit. (After Robertson.)
Genus AETEA Lamouroux, 1812.
The American Eocene deposits contain two species of this genus
which for lack of well-preserved specimens can only be referred to
the well-known recent species Aetea anguina Linnaeus, 1758 and A.
truncata Landsborough, 1852.