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The link provided by Petra describes the difference between the 2, a good read.
The X-ray luminosity of N70 is higher than that expected
from a quiescent superbubble model; thus, the interior of N70
is most likely heated by a recent SN. The X-ray luminosity
of N185 is an order of magnitude lower than that expected
from a quiescent superbubble with the size and expansion
velocity of N185. The hot gas in N185 is most likely originating
from a SNR, as it shows nonthermal radio emission, fast and
irregular expansion, and its X-ray luminosity is consistent with
that of an evolved SNR. The large shell of N185 may be
associated with an earlier SN event. These explanations are
supported by the observed stellar population in these two large
shell nebulae.
Ive attached my pic of N70.
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