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138 AjT/erican SeasheUs
4 to 4.5 mm.; glassy-white; depressed interspaces small, rounded; Texas
to the West Indies and Bermuda .
Family VITRINELLIDAE
Genus Vitrinella C. B. Adams 1850
sagraiana
Orbigny
Shell minute, thin, depressed, umbihcate, and with 3 to 4 subtubular
whorls. The umbilicus has rather flattened walls and is usually bounded by a
spiral cord. The rounded aperture is oblique, with a thin lip, its upper margin
arching forward. Columella only moderately thickened. Operculum corne-
ous, thin, multispiral. There are many species in American waters with
quite a number of genera and subgenera. The family is undergoing consid-
erable change under the current research by H. A. Pilsbry. We are including
only three examples of this interesting group. Consult recent numbers
of The Nautilus.
Subgenus Vitrinella s. str.
Vitrinella helicoidea C. B. Adams Helix Vitrinella
North Carolina to Florida and the West Indies.
2 mm. in diameter, planorboid, 4 whorls, spire moderately raised. Trans-
lucent-white, glossy, smooth. Umbilicus round, very deep, moderately wide,
bounded by a small, spiral, smoothish thread. Wall of umbiHcus flattish.
Columella strong, braced on the whorl above by a small, spreading callus.
Outer lip thin, sharp. Not uncommon in shallow water. This is the type of
the genus.
Subgenus Circulus Jeffreys 1865
Vitrinella multistriata Verrill Threaded Vitrinella
North Carolina to Florida.
Plate 17V
5 mm. in diameter, planorboid, well-compressed, 4 whorls, opaque-white,
with a glossy sheen. Outer surface covered with numerous, crowded, spiral,
incised lines. Umbilicus with rounded sides, deep, rather narrow. 50 to 100
fathoms. Locally common.
Subgenus Solariorbis Conrad 1865
Vitrinella beaui Fischer Beau's Vitrinella
North Carolina to Florida and the West Indies.