The first reverse (1827 - 1844), designed by William Wyon, features the figure of Britannia - the female personification of Great Britain; she is seated facing right, wearing a Corinthian helmet pushed back to reveal her face, resting her right hand on a shield bearing a saltire of arms, and holding a trident in her left hand. In the exergue, a rose, a thistle and a shamrock combined - the floral symbols of the constituent parts of the United Kingdom, respectively England, Scotland and Ireland.
The design is identical to that of the half farthing, farthing, halfpenny and penny coins issued in the same period. Typically for British coinage of the time, the denomination (or, indeed, the country of issue) is not spelled out on the coin. The various denominations can only be distinguished by size.
The second reverse (1866 - 1913), designed by William Wyon's son Leonard_Charles Wyon, shows at its centre, on two lines, the value and denomination in words: ONE THIRD FARTHING. Above that, St Edward's Crown. Named after Saint Edward the Confessor, it has been traditionally used to crown English and British monarchs at their coronations since the 13th century (with a two-century gap between 1689 and 1911). The shape of the crown was re-designed for the last two issues, (it was also changed on all the other British coinage).
Below the value, the date [year]. Around, a wreath of oak leaves tied below the date with a ribbon. Minor varieties exist in the number of leaves and acorns in the wreath.