Welcome to the forum James. Wow....nice bin 'o snakes you've got there. I'd have to agree with Don, your melanistic is probably a T.e.vagrans. To be sure I'd do some scale counts. T.e.vagrans has 19-21 rows of scales and has 8 upper labials with the 6th and 7th enlarged. T.s.sirtalis has 19 scale rows and 7 upper labials. Hope this helps.