Lesmosyne derives from the same root as Lethe and means exactly the same thing [ i.e., forgetfulness]. The sphere of the Muses, which arises from the primordial Goddess Mnemosyne, also has the benefit of Lethe, who makes everything disappear, that belongs to the dark side of human existence. It is only both the elements-giving illumination and letting disappear, Mnemosyne and her counter-pole, Lesmosyne-that make up the entire being of the Goddess, whose name comes solely from the positive side of her field of power. This is a union of the opposites under the dominion of the positive.

Karl Kerenyi, "Mnemosyne-Lesmosyne. On the springs of the Memory and Forgetting", in Casey Edward, Remembering, a phenomenological study, p.12