The size varies greatly up to 1¼ inches in diameter and 2½ inches in height. The normal shell is a steep-walled cone with numerous downward-pointing spines, giving it a "thatched" appearance. When crowded they take on a tubular form and may lack the spines. The base is membranous.
White in young or uncrowded individuals; otherwise dirty grey.
Coasts of Western North America and Japan. At about the quarter-tide level, on rock.
On the British Columbia coast this is the only large barnacle with a membranous base. It is usually found on the rocks, and much crowded.