The grunion, Leuresthes tenuis (AYRES) (family Atherinidae), a fish with a distribution limited to coastal southern California, U.S.A., and Lower California, Mexico, yielded the recently described copepod Caligus olsoni PEARSE, 1953, and still another parasitic copepod which proved to be an undescribed species of the genus Bomolochus. The species was collected by MR. ANDREW C. OLSON, Assistant Professor of Zoology at San Diego State College, who entrusted me with the material for description.