Carausius, AE antoninianus. London. 

IMP CARAVSIVS PF AVG, radiate, cuirassed bust right.
SALVS AVG, Salus standing left by altar, feeding serpent 
rising from altar, and holding sceptre.
B-E across fields.
Mintmark MLXXI

RIC V-2, London 155 var (bust type).
Rare