The horn shells are intertidal mud-lovers. The shells are elongate and with 10 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 Plate 19U West coast of Florida and the West Indies.
/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 Plate ipt
Texas, Louisiana and the West Indies. Not Florida.
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 Plate 19X
South Carolina to south half of Florida and the West Indies.
% 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
