This coin is interesting to me because Magnentius has more of a Constantinian look, like Constantine I or Constantius II. According to the mintmark, it was issued early in the revolt of Magnentius, so maybe the mintworkers did not even know what Magnentius looked like yet. The reverse has a bit of a double strike, but I think that it is an official Lyons mint coin versus unofficial. I have included a coin from the same series to show the difference in portraits.
Magnentius
A.D. 350-3
21x24mm 5.0gm
DN MAGNEN- TIVS P F AVG; diademed, draped, cuirassed bust right.
FELICITAS REIPVBLICE; Emperor standing left holding Victory on globe in right hand and labarum.
In ex. [F]PLG
RIC VIII Lyons 109