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Top Shell and Dolphin Shells — Part 1

Genus CHLOROSTOMA, Swains.

Shell conical, solid, base of columella toothed, aperture oblique, outer lip smooth within. A large genus, chiefly of Pacific coast species. It is fairly represented in the West Indies.

The Black Top Shell (C. funebrale, A. Ads.) is found in the greatest abundance upon rocks on the California coast. It has a heavy black shell, with distinct swelling of the body whorl below the suture. The apex is blunt, the umbilicus closed; the aperture is lined with greenish pearl; there is a white nodule at the base of the columella. The shell is an inch in height and width.

The Brown Top Shell (C. brunneum, Phil.), also a Californian species, is a clumsy brown thimble in form, about an inch long, with markings of white on the lips and a greenish pearly lining. It lives upon kelp and rocks.

The Snake-skin Top Shell (C. pellis-serpentis, Wood) is well named. The heavy, solid shell is 1 1/2 to 2 inches in diameter, a little higher than broad. Its crowded coils are separated by linear sutures, and finely marked with dark patches in intricate patterns on yellow or pink ground colour. The aperture is lined with pearl; the columella bears a heavy tubercle in the middle, and a small tooth where it joins the thin lip of the aperture.

Habitat.--Gulf of California to Panama.

Genus NORRISIA, Bayle

Shell large, round, umbilicated, solid, smooth; spire depressed, conical; whorls few, rapidly enlarging; aperture quadrangular; outer lip sinuous, thin edged; columella sinuous. An isolated genus of one species.

Norris's Top Shell (N. Norrisii, Sby.) is a common species, living upon the giant kelp on rocky beaches southward from San Francisco. The dome is depressed and tipped over by the enlarged body whorl. The apex is blunt; the sculpture consists of faint radiating lines. The colour is a rich brown turning black at the mouth of the wide umbilicus which has a greenish lining rim. The lip is thin-edged. The aperture is large and lined with pearl. A shaggy coat roughens the outside of the operculum; inside it is smooth and multi-spiral, with a central nucleus.

This species is abundant about San Diego, where it is often seen in tide pools, with the strawberry-red body extended, crawling on seaweed. Shells are picked up on the beaches after violent storms. It measures one to two inches in altitude, and about two inches in diameter.

Habitat.--Southern California.

Genus CALLIOSTOMA, Swains.

Shell pyramidal, with beautiful colouring and sculpturing; base flattened. A large genus of unusually beautiful shells.

The Ringed Top Shell (C. annulatum, Martyn) is a specimen people are always interested in collecting. It is abundant in many places along our Pacific coast. Its shell is fragile, and can only be collected in fine weather, and then by going out in a boat and gathering the seaweed to which these delicate creatures cling. In bad weather they sink to the bottom. Fragments are picked up on the beach, but rarely a perfect shell. The whorls are yellowish, ornamented with raised brown dots in parallel rows; the depressions between the whorls and the area about the axis are shaded with purple. The exterior is almost as beautiful as the pearly lining. Height,1 inch.

Habitat.--California.

The largest American species is C. canaliculatum, Martyn, an inch and a half high. It is conical; its revolving ribs sharpedged and separated by spiral canals, which, however, are not purple. The ribs are pale yellow or ashy, the depressions brownish.

Habitat.--Pacific coast.

The Blue Top Shell (C. costatum, Martyn) is the abundant species along the northern Pacific cost. It is conical, with a sharp apex, rounded whorls and flattened base. The whorls are ornamented by parallel yellow riblets separated by brown depressions. The aperture is round and beautifully pearly; the columella simple.

This shore-dwelling species has a heavy shell. A dilute acid bath and a scrubbing removes the outer layer and exposes the blue pearl that forms the shell substance. The living mollusks crawl on rock surfaces exposed by the tide, but remain in the dark if possible. Length, 3/4 inch.

Habitat.--California northward.

C. gemmulatum, Cpr., is wound with strings of granules, each whorl bearing two principal rows, and many small ones. The gray surface is streaked with dark brown from the apex downward. Height, 1/2 inch.

Habitat.--Southern California.

Several recently named species have been discovered by collectors dredging in deep water off the California coast. All are easily recognisable as top shells by their characteristic form.

The Pearly Top Shell (C. occidentale, Migh. and Ads.) of the Maine coast is strongly ribbed, with a row of white dots ornamenting the pearly surface of the upper half of each whorl. It is but half an inch long, and is only obtained by dredging in gravel off shore.