THE OLIVE SHELLS. RICE SHELLS. HARP SHELLS - FAMILY OLIVIDAE Shell cylindrical or fusiform, spiral, highly coloured, por celanous, polished; without epidermis; columella, lip, sutures and spire more or less covered with enamel deposits; outer lip simple; aperture long, obliquely notched below; operculum small or wanting; foot large, grooved above, with semi-lunar extension in front; posterior end prolonged into a point; mantle reflected over shell, forming large, tubular siphon in front, and a whip-like prolongation behind, which lies in the spiral, grooved suture; radula present; eyes borne on tentacles, or wanting. A tropical family, including few living genera.
Genus OLIVA, Brug.
Shell oblong, smooth, thick, heavily enameled, without epid ermis, colour laid on in two layers in different patterns simul taneously by mantle folds; spire short; suture canaliculated; columella plaited; aperture long, operculum wanting. A tropical genus of about a hundred species, distributed chiefly in Central America, the Philippines, Mauritius and Ceylon. This is one of the genera in which the foot secretes the shell, at least in part.
It is a trick of some shell dealers to remove with acids the outer surface of an olive shell which exposes a layer with quite different pattern. The shell may now be palmed off on an in experienced collector as a different species or a freak of nature.
The Red-mouthed Olive (0. erythrostoma, Lam.) has one dependable character, the deep orange-red aperture, but its exterior varies surprisingly, forming several distinct varieties. The shell is thick, heavy and somewhat swollen, below the pointed spire. The surface generally bears more or less distinct wide revolving bands. The pale creamy ground is sometimes covered 9T The Olive Shells. Rice Shells. Harp Shells almost to the lip by deep chocolate, banded with chestnut. At the other extreme the shell is china-white, faintly mottled and banded with fawn colour or violet.
Different schemes of painting intermediate between the very dark and very light forms are seen in a moderately complete series of shells. These mollusks inhabit muddy sand in deep water. Length, 2 to 3 inches.
Habitat.—Ceylon and the Philippines.
The Moor Olive (0. maura, Lam.) is one of the commonest and most variable species in the genus, and one of the handsomest. It may be known by the tumidity of the shell toward the depressed spire, and the callosity at the posterior end of the rather wide white-lined aperture. There are forms with burnt orange ex terior, faintly banded. Others are deep grayish chocolate of almost solid colour. Olive forms with flame-like streaks of deeper shade in broad bands are common. Lamarck's type was uni formly dark-coloured; the streaked, zigzagged and mottled forms he called varieties. The base of the columella has a tinge of red in nearly all of these forms. Length, 2 to 2/ inches.
Habitat.— Indian Ocean to Australia.
The Tiger Olive (0. tigrina, Lam.) is smaller and broader, with fine dark blue dots sprinkled thickly over an ash-coloured ground. The interior is white. A dark brown form is also described.
Habitat.— East Africa to Philippines.
The Two-plaited Olive (0. biplicata, Sby.) is a thin, smooth, bluish-gray shell, its suture brown. in size and form this shell is very like an olive. The blue occasionally gives way to dark brown or olive; some forms are nearly white. The aperture and the wide callus on the columella are violet-tinged. Two distinct folds on the base of the axis justify the name.
These little mollusks gather in companies just below the level of the sand, burrowing for food with siphons at .the surface for fresh water. Professor Keep says they migrate rapidly, and a "school" of them is not easily located. He found them once by thousands on a beach, directly after the tide had left it. He says: "You must go at the very lowest morning tide, and search till you find their beds. . . . I took some of them home and put them in a jar of beach sand and sea water. The plough shaped foot quickly digs a hole in the sand, and the long breathing 92 The Olive Shells. Rice Shells. Harp Shells siphon which curls up through the canal and reaches through the sand up to the clear water, is like the trunk of a swimming ele phant." I have found them just under the muddy sand along the breakwater at San Pedro, but not in companies, as Professor Keep did.