E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Who eats oysters on St. Jamess Day will never want. St. Jamess Day is the first day of the oyster season (August 5th), when oysters are an expensive luxury eaten only by the rich. By 6, 7 Vict., c. 79, the oyster season begins September 1, and closes April 30.