I have several of these shells, and they are impossible to identify exactly.
However, take a look at Eddy Hardy (he's pretty much up to date):
http://www.gastropods.com/6/Shell_1026.shtml    (nigrispinosus)
http://www.gastropods.com/6/Shell_5776.shtml    (ternispina)

If you can't tell the difference, then join the rest of us. Perhaps there
is a unique feature of one of them that differentiates, but otherwise, I
think it is a question of synonymity that no-one has yet looked  into.

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