The Sydney mint reverted to the Imperial St George and Shield designs in 1871 with the Shield design intended for export to other colonies. The fourth reverse design features a short length tail as opposed to the long tail used since 1871 and the medium tail used since 1874 as in the illustration below:
This type differs from the other St George reverse designs by having a wider truncation at the base of the bust of her Majesty Queen Victoria.
The origin mint of this issue can be determined from the mintmark beneath the bust on the obverse :