Mythologically speaking, there's but one Lamia, a Libyan queen who was only stated to steal kids and look monster-like. The snake-like shape is only one of those interpretations, just like how they're sometimes portrayed as bloodsucking beings. I would like to know why it's now associated with nagini when Melusine could be a more fitting reference. I read this happened over time (possibly, literal centuries), what with the "lamia is now a race" and "lamia is so and so". As someone who likes mythology, this is something I'd love to understand better. I guess that's why, when it comes to mythology, I would like to learn from the likes of Chiron, Mímir or Dian Cecht -as I could do with some medical knowledge-.