THE KEY-HOLE LIMPETS - FAMILY FISSURELLIDAE. Shell broadly conical, elevated or flattened, not pearly, with apical or anterior anal slit, or hole; operculum wanting; gills, a pair, symmetrical; head well developed, with short muzzle, eyes on outer bases of tentacles on rudimentary stalks; siphon occupying notch or hole; foot fleshy, with fringed border.
This large family contains more than a dozen genera and over one hundred species. The slit or key-hole distinguishes the adult shells from those of the limpets proper. In habits the mollusks are much like Acmma and Patella.
The young key-hole limpet begins life with a spiral shell and a marginal slit. Gradually shelly matter is added which unites the margin below the slit, and the spiral seems to uncoil. It finally disappears, the slit having travelled upward and replaced it at the apex of the shell.
Genus FISSURELLA, Brug.
Shell steeply conical, limpet-like, but with hole in apex, bounded internally by a thickened band or callus ; lining white, porcellanous; body when at rest contained in the shell.
The Volcano Limpet (F. volcano, Rve.) is sig nificantly named. Its steep cone looks like the ash crater of the typical volcano of our geographies. A touch of realism is added by the red stripes that radiate from the apical hole, like streams of molten lava pouring down the sides.
Shells of this species are common on beaches of Southern and Lower California. Very strangely, dead and worn shells are much brighter than living ones. They are ashen pink with purple rays when alive; the mantle is striped with red and the foot is yellow. They creep about on the rocks, and may be seen at low tide.
Genus LUCAPINA, Gray Shells large, thick, flattened, oblong-oval, finely ribbed and cross-banded, apex slightly in front of the middle, perforated by a large hole, bounded inside by a rounded callus; body large, black, like india-rubber, too big to be contained in the shell when at rest; the reflexed mantle engulfing the shell when active; edge of the mantle smooth; foot fringed; tentacles long; eyes prominent.
The Great Limpet (L. crenulata, Sby.) is easily
the giant of the family. It is four to five inches long,with a broad, apical hole, often one inch long. The thick shell is white inside and smooth. The outside shades from pale buff to gray, and is marked by small but distinct radiating ridges, crossed by many concentric lines, grouped in bands showing the stages of growth. The finely scalloped border is the shell's chief beauty.
Keep describes the mammoth creature that finds this shell inadequate to contain it. It resembles a brick in form and size. The huge foot is yellow, with the black mantle outside.
Habitat.— Monterey to San Diego, California.
The Limpet (Megatebennus bimac ulatus, Dall) is a common shell on beaches from Monterey south. It is strongly ribbed from the large apical hole to the margin, and white except for two triangular spots of black on opposite sides.
In form this little limpet shell resembles that of the giant Lucapina. The animal, however, is much smaller in proportion, though the mantle is able to cover the shell completely. Length, I inch.
Genus GLYPHIS, Cpr.
This genus is separated from Fissurella (which its shell resembles externally) by the sudden posterior cutting off square of the callus that bounds the apical hole inside the shell. The 228 The Key-hole Limpets central tooth of the radula is wide. It is by internal characters proved to belong in the group with Emarginula, which has the apex usually closed, with the slit between it and the margin. The little "chopped off" end of the inner rim of the hole is the sign by which shells of this genus are best recognised.
Habitat.—Chesapeake Bay to the West Indies.
The Rough Key-hole Limpet (G. aspera, Eschs.), a peaked key-hole limpet of the Pacific coast, is the largest species of its genus; the oval shell is over two inches long. Its dirty white exterior is radially streaked with regularly widening dark bands, and ridges that have thin, sharp blades. The apical hole is almost round, and very thick-walled.
Habitat.— Sitka to Monterey Bay.