Mike, I do not understand the assignment of this to subspecies H. m. marginata. The only image I can locate of that subspecies is at Cerambycidae of Florida.
Yanega pictures H. m. ardens, which looks similar to my images, other that in mine, there is no orange on the humeral angle of the elytra. (However in a lateral view of the mating pair I have, you can see a bit.) Yanega says this extension onto the elytra is present "sometimes" in ardens.
Evans (1) used my photo below (taken nearby to these) for his illustration of H. m. ardens:

He says that H. m. marginata has "dense elytral pubescence along sides and suture" as does the photo of H. m. marginata from Cerambycids of Florida. I think all my photos from Durham NC are H. m. ardens. They lack the pubescence described by Evans and present in the Florida Cerambycids specimen.