A silver coin (23.5 mm diameter with milled edge) featuring a crowned and robed bust of George V facing left; around, GEORGIVS V D.G. BRITT: OMN: REX F.D. IND: IMP: ; below bust in small lettering the artist's initials B.M.
The reverse features the Ensigns Armorial of the Commonwealth of Australia, as authorised by Royal Warrant 7th May 1908 - composed of a simple shield enclosing a cross of Saint George on which are five six-pointed stars, around the outside of which are six small escutcheons, i.e., small shields. The shield is supported by a kangaroo and an emu standing on a grassy mound. Above the shield a crest, the seven-pointed star of Federation on a wreath. Below on a ribbon the motto ADVANCE AUSTRALIA is inscribed. Around above, ONE SHILLING and below, between arrow heads, the date, 1919. Below the date is the mint mark M.
No regular shilling coins were issued dated 1919, this is an experimental piece produced as part of planned debasement of the silver alloy (0.625 silver). The debasement, in the end did not occur.
According to The Australian Coin Chart 1966 "A few Pattern Shillings dated 1919 and 1937 have been reported and would realise over £500 at Auction".
Greg McDonald's "Australian Coins and Banknotes" catalogue calls this an "unissued circulation strike".
The "Renniks Australian Coins and Banknote Values" catalogue (Pocket Edition 1986) says: "Only two specimens are known to exist. One in Science Museum Victoria and specimen sold ex Spinks [1981, for $40,000]. The two known coins have been punched in the field of the coin with two small S's on the obverse and reverse to officially denote that they are specimens and to distinguish them from the currency issue. None were issued for circulation."
It has to be noted though that the specimen in the photo belonging to Museums Victoria (ex Science Museum Victoria) does not have said S punch marks.
According to Remick's "Catalogue of British Commonwealth Coins 1649-1971", 4 specimens are known. Krause 1988 Edition lists 6 pieces, later editions show mintage as unknown.