A lot of S. furcata show a hint of a dark margin, and some show it strongly. In S. fasciata it is usually quite pronounced though, and more developed than in all but just a few S. furcata (it is pretty faint in this particular one). There are other differences, notably the shape of the pronotum seems to be somewhat different, with a straighter margin at the sides of the top, and the top itself a bit narrower and more convex in profile (somewhat "saddle-shaped") in S. fasciata - flatter in S. furcata. The pale stripes on the top margins of the pronotum tend to be narrower and more sharply defined in S. furcata. And, so on.

However, to be honest, I'm not sure how reliable these differences really are (for instance some S. furcata from Texas look a lot like S. fasciata from the Northeast). It could be that S. fasciata is wider ranging than believed; it could be that they are really just variants of one species; or, it could be that there are more species involved than anyone has recognized. Some specimens are hard to place (at least from photos alone).

One of my sentences switched direction in the middle, so I should clarify.

" There are other differences, notably the shape of the pronotum seems to be somewhat different, with a straighter margin at the sides of the top in S. furcata, and the top itself flatter. In S. fasciata the top is a bit narrower and more convex in profile (somewhat "saddle-shaped"). "

I spent a fair bit of time looking at different individuals of several species to get a sense whether there were other differences this morning. This clarification is very useful.