The normal-shaped shell may be 2 or 3 inches in diameter and 4 to 5 inches in height. The opercular opening is large and has a jagged edge. The beak of the tergum projects above the edge of the opening. Well-developed ribs are present in young specimens, but they tend to become obscured by erosion in older individuals. The base is calcareous and porous.
Dirty white with pink parietes in some young specimens. Cinnamon buff on the interior of the cover-plates; a purple patch usually near the beak of the tergum.
Southern coast of Alaska south to Monterey Bay, California. Below low-tide level, usually in 10 to 20 feet of water; occasionally down to 30 fathoms.
This is the largest barnacle found on the Pacific Coast of North America. It is often found in large groups of individuals growing upon one another, and frequently it grows on the holdfast of kelp. Such individuals are occasionally cast ashore attached to kelp which has been broken loose by storms.
When crowded this barnacle gains room by deepening the base. Shells of large specimens are usually eroded so that the external sculpture cannot be seen. Boring sponges also tend to erode the shell.
A large barnacle outwardly identical with Balanus nubilus has been described as a distinct species, Balanus altissimus (Cornwall, 1936). Though it differs in the arrangement of the nervous system and occupies a position on the rocks above low tide, it may be only an environmental variety of B. nubilus .