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152 American Seashelh
The horn shells are intertidal mud-lovers. The shells are elongate and
with lo to 15 convex whorls. Axial ribs are more prominent on the early
whorls. Outer lip flares. Operculum horny, thin, paucispiral and with its
nucleus at the center.
Subgenus Cerithideopsis Thiele 1929
Cerithidea costata da Costa Costate Horn Shell
West coast of Florida and the West Indies.
Plate 19U
/4 inch in length, translucent, pale yellowish brown. With 9 to 1 2 very
convex whorls. Axial, curved ribs are round and distinct on the early whorls,
fading out on the last two whorls. No old varices present. A common
shallow-water, mud-loving species.
The subspecies C. costata turrita Stearns, the Turret Horn Shell from
the Tampa-Sanibel region, has 15 to 20 (instead of 25 to 30) axial ribs on the
next to the last whorl.
Cerithidea pliculosa Menke Plicate Horn Shell
Texas, Louisiana and the West Indies. Not Florida.
Plate ipt
I inch in length, brownish black in color. 11 to 13 slightly convex
whorls. Several yellowish, former varices are present. Numerous spiral
threads make the axial ribs slightly nodulose. Locally common. It may yet
turn up in northwest Florida.
Cerithidea scalari^orvns Say Ladder Horn Shell
South Carolina to south half of Florida and the West Indies.
Plate 19X
% to I % inches in length. Pale russet-brown to slightly violaceous, usu-
ally with many conspicuous, dirty-white, spiral bands. 10 to 13 moderately
convex whorls. Many coarse, axial ribs present which stop abruptly below
the periphery of the whorl at a sharply marked, rounded spiral ridge. Base
of shell with 6 to 8 spiral ridges. No former varices. Common on mud flats.
Cerithidea hegeivischi cali^ornica Haldeman California Horn Shell
Bolinas Bay, California, to Lower California.
I to I /4 inches in length, resembling our photo of C. pliculosa from the
Atlantic (pi. i9t). Whorls 11, spirally and weakly threaded, and axially
strongly ribbed (12 to 18 ribs per whorl). Dark-brown in color with i or