Tacitus AE Antoninianus. Rome mint. 

IMP CM CL TACITVS AVG, radiate draped, cuirassed bust right.
SALVS AVG, Salus standing left, feeding serpent rising from altar.
Mintmark XXI delta.

Estiot 128, La Venera 1855; RIC 93 var (Salus standing).

AAH ebay sale.