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166 American Seashells
/4 to I inch in size, cap-shaped, dull-white, and with an internal, delicate,
deep cup which has its anterior third neatly sliced away. The base of the
cup is attached near the center of the inside of the shell but slightly off in
the direction in which the apex of the shell points. Exterior has small, axial
corrugations or tiny cords, rarely spinose. Nucleus minute, spiral and glassy-
white. Uncommon except in the West Indies.
Genus Hipponix Defrance 1819
Hipponix antiquatus Linne White Hoof-shell
Peru.
Plate 2 It
Southeast Florida and the West Indies. Crescent City, California, to
/4 inch in size, white, heavy for its size, cap-shaped, and usually with a
poorly developed spire which may be located either at one end of the shell
or near the center. The nuclear whorls are spiral and glassy-white. There
is a horseshoe-shaped muscle scar inside the shell. Axial sculpture of promi-
nent, rugose ribs which are crossed by microscopic, incised lines. Periostracum
absent or very thin and light-yellowish. Moderately common. Found cling-
ing to rocks and other shells.
Some Pacific northwest specimens are limpet-like in shape, flattish, cir-
cular, gray-white, with the apex near the center of the shell, and with smooth-
ish, strong, circular cords (form cranoides Carpenter). Another form bears
foliaceous concentric lamellae which are finely striate axially {serratus Car-
penter from Monterey to Panama).
Hipponix subrufus subrufus Lamarck Orange Hoof-shell
Southeast Florida and the West Indies.
V2 inch in size, similar to antiquatus, but usually stained with light orangebrown,
and with numerous, small spiral cords crossing concentric ridges of
about the same size. This frequently gives a beaded surface. Periostracum
fairly heavy, tufted and light brown. Moderately common.
Hipponix benthopbilns Dall (Dall's Deepsea Hoof-shell) is well-spired
in one plane and is entirely smooth. It is rare and comes from deep water
off" Florida and throughout the West Indies.
Hipponix szibruftis tiimens Carpenter Pacific Orange Hoof-shell
Crescent City, California, to Lower California.
Very close in characters to the Atlantic subrufus subrufus, but the shell