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150 American Seashells
plug dome-shaped with a tiny pimple on one side. Color translucent-tan to
light-brown. Old specimens are whitish, often with a purplish stain. The
shell has a white band behind the aperture. C. hemphilli Bartsch and C. bakeri
Bartsch are probably diminutive forms of this species. The development of
the small pimple on top of the dome-shaped plug is variable.
Subgenus Meioceras Carpenter 1858
Shells 2 to 4 mm. in length, very bulbous in the middle, smooth, and
with an oblique, constricted aperture. Resembles a miniature Cadulus
(Scaphopoda).
Caecum nitidwn Stimpson Little Horn Caecum
Southern half of Florida and the West Indies,
Figure 376
2.0 mm. in length, glassy translucent-white with irregular specks or mot-
tlings of chalk-white; bulbous in the center; apex with a lopsided, rounded
plug which has a tiny projection on the highest side.
Caecum lennondi Dall from the west coast of Florida differs in having
a single, moderately well-raised, circular hump around the middle of the
shell. Uncommonly dredged just offshore.
Family PLANAXIDAE
Genus Flanaxis Lamarck 1822
Planaxis lineatus da Costa Dwarf Atlantic Planaxis
Lower Florida Keys and the West Indies.
/4 inch in length, thick and strong; glossy-smooth when the thin, smooth-
ish, translucent periostracum is worn away. Color whitish cream with neat,
spiral bands of brown (10 in last whorl, 5 showing in whorls above). Whorls
in top of spire with 4 or 5 small spiral cords, later becoming obsolete. Aper-
ture slightly flaring, enamel-white with 10 brown dots on the edge of the
outer lip. Nuclear whorls very small, glossy, translucent-brown and sharply
pointed.
Subgenus Supplanaxis Thiele 1929
Planaxis nucleus Bruguiere Black Atlantic Planaxis
Southeast Florida and the West Indies.
H inch in length, resembling a thick, polished, dark-brown Littormu
periwinkle. Characterized by 5 strong spiral cords which are developed on