Common Lampshell, Terebratalia transversa.

This small, 18mm across, shell is not a Mollusc but is in a phylum of its own, Brachiopoda. In our area the shells have prominent ribs as opposed to the smoother shells of more southern lamp shells. The Lampshell is attached to the underside of a large rocks at the very low tide line and much deeper. The flexible foot exits the shell at that rear aperture. My next challenge is to find a live specimen. When’s the next low, low tide?
https://inverts.wallawalla.edu/Brachiopoda/Class Articulata/Order Telotremata/Terebratalia_transversa_Page.html
From Eugene Kozloff’s “Seashore Life of the Northern Pacific Coast” (1983),
“A particularly attractive variant is common on Saltspring Island, in the Canadian San Juans, and perhaps elsewhere in the same general region. The shell is strongly ribbed, and the width is much greater than the length.”