June Lockhart, who became a mother figure for a generation of television viewers whether at home in “Lassie” or up in the stratosphere in “Lost In Space,” has died. Lockhart died Thursday of natural causes at her home in Santa Monica, family spokesman Lyle Gregory, a friend of 40 years, said Saturday. The daughter of prolific character actor Gene Lockhart, Lockhart was cast frequently in ingenue roles as a young film actor.