The valve of a Pointed Macoma (Macoma inquinata), which I found at Sunset State Beach in southern Santa Cruz County, CA. Note the valve's ovate shape with slightly off-center umbo, the two cardinal teeth with no lateral teeth, and the deep palial sinus that almost connects the two adductor muscle scars.
Valve dimensions: 3.9 cm X 2.5 cm.
Length 4cm. ID'd From Kozloff - valves not perfectly oval, pointed towards posterior end and rounded towards anterior, do not show posterior bend to right. Outside of valve white-ish (not pink/yellow/blue), periostracum brown and NOT polished or transparent.
Macoma genus looks like the closest match from the book I have.
This pink bivalve, about 1" X 2", may be a Baltic Macoma, found at low tide in the intertidal of this lagoon.