Tacitus, 25 September 275 - 12 April 276 A.D.

Obverse:
Laureate, draped and cuirassed bust right

AK K Λ TAKITOC CEB

AK: AVTOKRATOR is the equivalent of the Latin Imperator, 'emperor'.
K Λ is an abbreviation for K AV IOC, 'Claudius' transliterated into Greek.
TOK: TAKITOC= Tacitus
CEB: SEBASTOS (greek indication for augustus).

With the pellet between TOC . CEB

Reverse:
ETOVC A (year 1)

Dikaiosyne standing left holding scales in right hand and cornucopia in left. Diakaiosyne is the Greek equivalent of Aequitas ('Equity, Fair Dealing' to quote Sear).

Domination: Billon TETRAdrachm (4 drachms): size 21 mm

Mint: Alexandria, provincial.

Comment:
These Egyptian issues are not in RIC, but the old standard catalogue for these is Milne, where yours is no. 4492, with the pellet between TOC . CEB. They are also listed in the new Sear vol.III (though in not as much detail), where the nearest is 11831, which doesn't have the pellets in the obverse legend (Milne 4489). Other references : Curtis 1832, BMC 2403v ; Geissen 3115.