While Tulsa OK would be just inside the range map Gordon(1) provides B. felina, 5mm is way too big and the body form, at least of the female, appears more oval/elongated than round (compare with the dorsal shot of Will's female). That said, B. ursina's range map stops about mid-Arkansas (and size is listed at 3.0-4.0mm). It's great Sam has both a male and female imaged here, but the features on these two species are still very similar. I'd lean toward B. ursina, even with the location, if I had to call it.

Ok, but as far as the size, I didn't measure them so 3, 4, 5 mm isn't that much off, especially when you consider the critter(s) is trying to escape at the same time I'm taking pics.