|Abstract||L. microlepis ranges from Baja California [Mexico] to Peru, a distribution shared with L. negropinna and L. pardale. Unlike its more shallow-dwelling congeners, L. microlepis exhibits marked latitudinal variation in meristic and morphometric characters and in certain features of pigmentation. Three well marked subspecies are defined, 2 of which, L. microlepis hubbsi and L. microlepis inca, are described as new. The isolating mechanisms involve the fact that adults of L. m. microlepis occur in cold waters of the deep shelf and upper slope while the larvae require warm surface waters as do all species of Lepophidium. Unfavorable surface currents which move larvae offshore, surface temperature and its annual variation, poleward-flowing undercurrents, and physiographic features of the Continental Shelf itself are all discussed as factors in maintaining stock isolation of one or all of the subspecies. Surface currents are most important in isolating L. microlepis from L. m. hubbsi. Reasons for the isolation of L. m. hubbsi and L. m. inca are less clear but probably involve the marked difference in surface temperatures between the range of the 2 and surface currents and possibly the Peru-Chile Undercurrent.