An example of a recent tubiform fossilGirvanellais reported from a transitory, freshwater flash‐spring, in an area of the Borrego Desert, near San Diego, California. It occurs as the preserved, calcite‐impregnated sheath of the blue‐green algaPlectonema gloeophilumBorzi. In size and form, the fossil is identical to the first specific description of a recentGirvanella.The data presented give strong support to the idea of specificity for calcification in some blue‐green algae.