according to notes on Bugguide.net (see below), if you take the sum characteristics, you can get a good prob. ID. I think I have a fairly high probability of correct ID on this one.

There are no 100% consistent diagnostic characteristics in wing maculation or spots/no spots on the patagia (the "collar"), to reliably distinguish nais/carlotta/phalerata/vittata. The only full-proof method is dissection and examination of genitalia (the exception is in male phalerata, in which the valve is easily distinguished by its longer, up-curved apex. So one could brush the scales away from the last sternite and see it without dissection. The nais/carlotta/vittata group have rather blunt and rounded apices of the valve.)
However, within this group, using the sum of typical (although not necessarily diagnostic) characteristics, can allow for a reasonably probable species ID.