Commonwealth coinage, demonetised in 1661-2. On the reverse side they featured the English cross and the Irish harp.
The Commonwealth coins (stamped with the cross and harp, and the inscription, “The Commonwealth of England”) were called in by proclamation, September, 1660, and when brought to the Mint an equal amount of lawful money was allowed for them, weight for weight, deducting only for the coinage (Ruding’s “Annals of the Coinage,” 18 19, vol. iii., p. 293). The harp was taken out of the naval flags in May, 1660.
This text comes from a footnote on a diary entry in the 1893 edition edited by Henry B. Wheatley.
harp and cross crowns.
shows images of these coins. They were popularly known as 'breeches' coins for reasons that are apparent when you see the images.
Note that there are underscores (not easily visible in this link) on either side of the hyphen and also between 'gold' and 'crowns'.
Harp and Cross money (Commonwealth coins)
Chart showing the number of references in each month of the diary’s entries.