When I Googled "green crayfish" I got lots of items several of them were asian species which I hope and assume you did not receive from Hartley's.
Crayfish species are identified and separated using features of the claws (chelae), shape of the rostrum (snout), shape of the areola (hour glass marking on carapace-back of shell), and shape of gonopods (sperm transfer structures). Genrally to the untrained person all crayfish look basically alike unless they have some unusual distinctive features.
One pretty good website for crayfish from central US is:
http://mdc.mo.gov/nathis/arthopo/crayfish/varcraw.htmIf someone would send me a "green crayfish" preserved in rubbing alcohol, I would identify it.
