This comes too late for the discussion, but others looking here for info in the future may be interested in this screed on the origins of lamia in mythology and in D&D, at Cayzle's Wemic Site.
It discusses the greek myth of Queen Lamia, the evolution of the mythological figure into a monster used to scare children, Keats, old beastiaries, snake and lion versions, and images of lamias from diverse editions of D&D.
A google search for cayzle's wemic site gets you to my home page, and then search for "lamia."