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Limpets

From San Francisco north and south the type diverges, becoming more strongly ribbed behind the apex as we go north, and tending to smaller and narrower ribs and more spreading sides as we go south. It is an exceedingly variable species. Length, 1 inch.

Habitat.--Sitka to Lower California.

The Shield Limpet (A. pelta, Eschs.) has an oval, shieldshaped shell, with pointed apex near the centre, and low, coarse ribs radiating from it. A narrow black band follows the edge of the lining, which is oftenest made up of scallops or disconnected square spots. The peak is more elevated than usual in a small form found near Olympia, living on the valves of mussels. The typical colouring is gray, striped with black, often tesselated. Length, 2 inches.

Habitat.--Aleutian Islands to Southern California.

The White Cap (A. mitra, Eschs.) has a creamy smooth shell, rounded up to a decided peak. The dead shells are often picked up on Pacific beaches, but the mollusk is rarely seen alive. It is scarcely an inch in height, and slightly more than an inch across the almost circular base.