It seems to me that there are at least two different loops that look like supernova remnants (or some other kind of shells). Is anyone familiar with the physical nature of both of these loops?
One of these loops touches Rosette Nebula and includes a filament that is called "Monoceros Loop" in the Interstellarum Deep Sky Atlas, page 60, RA = 6h43m, DE = +6.5°. But there is a second loop around Cone Nebula and Hubble's Variable Nebula that looks like a more homogeneous shell (perhaps not a supernova remnant?).
@Jiri and others: I would love to read about your visual observations. :-)