THE incessant, raucous barking in air by the California sea lion (Zalophus californianus) is well known. Wenz1 presented sonograms of barks from Zalophus which were recorded during the breeding season by an underwater hydrophone at a depth of 360 feet, about 2 miles off the shore of San Clemente Island (60 miles from the coast of Southern California). These barks (like those recorded in air) were characterized by a rich harmonic structure, and an up–down–up frequency modulation, and sometimes terminated in a high upward sweep. Wenz thought that it was unlikely that these barks originated entirely in air and suggested that they were transmitted into the water by vibration of the submerged throat area while the sea lion's nose and mouth were in air.