Bulletin - United States National Museum - Smithsonian Institution

SOUTH AFRICAN MARINE MOLLUSKS.
Genus CYCLOSTREMA Marryat.
CYCLOSTREMA ALFREDENSIS, new species.
Plate 35, figs. 6, 7, 8.
169
Shell small, milk white. Nuclear whorls two and one-half, well
rounded, smooth. Post-nuclear whorls marked by four strong
spiral keels, of which the first, which is the weakest, is a little anterior
to the summit, while the second marks the very strong shoulder,
the fourth forming the peripheral keel, and the third being half way
between the second and the periphery. In addition to these spiral
cords the whorls are marked by decidedly retractively slanting axial
riblets which increase in strength and spacing as the shell progresses
in size. About 25 of these occur on the last half of the last turn.
These riblets cross the sulci, which are about twice as broad as the
spiral cords, but do not seem to pass over the spiral cords. Periphery
rendered angulated by the peripheral cord. Base well rounded,
marked by three spiral cords, of which, the third and strongest bounas
the moderately large umbilicus ; the other two divide the space between
this and the peripheral cord into three equal parts. The deep sulci
are marked by the continuation of the axial riblets. Aperture
oblique, subcircular; outer lip rendered decidedly sinuous at the
margin by the external sculpture, which is also apparent through
the substance of the shell; inner lip oblique, slightly curved and
slightly reflected.
The type, Cat. No. 250501a, U.S.N.M., comes from Port Alfred
(Coll. No. 1374). It has one and one-fifth postnuclear whorls, and
measures: Altitude, 1.2 mm.; greater diameter, 1.7 mm.
Genus CYCLOSTREMELLA Bush.
CYCLOSTREMELLA FARICA, new species.
Plate 32, figs. 7, 8, 9.
Shell small, depressed helicoid, very thin, translucent, bluish
white. Nuclear whorls a little more than one, well rounded, smooth.
The first half postnuclear whorl is ornamented with a strong keel a
little anterior to the summit and another a little posterior to the
periphery; the spaces between the keel and the summit, and between
the keels are finely striated. These striations become stronger and the
keels less pronounced after passing the first half turn, until on the
final whorl the shell is marked with numerous equal and equally
spaced fine spiral lirations, of which the first two near the summit
are a little weaker than the rest and give this narrow portion almost
the appearance of a smooth band. About 40 of these lirations occur
between the summit and the periphery. Sutures well impressed.
Periphery well rounded. Base strongly rounded, with a broad
umbilicus which extends over half of the diameter of the base. The
outer limit of the umbilicus is marked by a strong spiral cord; another