Hi,
No, I think it can't be Basil, because there's only one S in that name. I think the unclear letter must be N completing BAC/CIAN/OC. The
portrait likely depicts the owner of the seal, whose name was
Bassianus. The
portrait looks 4th century to my eye, and I would propose to date it to the 2nd half of the 4th century. There are several persons named
Bassianus for this period (a notarius of the East 371/72, a prefect of
Egypt in 379 and a rationalis
rei privatae in 384), any of whom could be the other owner - or of course another
Bassianus unknown from other sources.
Regards
Gert