Guineas were a specific weight of gold, rather than a unit of currency. The coins were a way of saying "I (bank) confirm this coin ways X and is of Y purity".

Here's what I've found :

In 1663 the Royal Mint was authorized to coin gold pieces of the value of 20s. `in the name and for the use of the Company of Royal Adventurers of England trading with Africa'; these pieces were to bear for distinction the figure of a little elephant, and 44 1/2 of them were to contain 1 lb. troy of `our Crowne gold'. The 20s. pieces of the African company received the popular name of guineas almost as soon as they were issued, as being intended for use in the Guinea trade, and made of gold from Guinea; and the name was extended to later coins of the same intrinsic value. As silver was the sole standard till 1816, the value of the guinea was from the first subject to market fluctuations, according to the condition of the silver coin, which became so bad that the guinea rose as high as 30s. in 1695. In Dec. 1717 it was fixed at 21s., after which it underwent no further alteration. The latest coinage of guineas took place in 1813; the sovereign, of the value of 20s., was first issued in 1817.

Sounds like a scam, Nilly. Like New Coke.

Actually, come to think, USian money divides kind of funny, or used to. I've never seen a bit-coin, but they must have existed, since the song goes "Shave and a hair cut, two bits" (i.e., $0.25. A bit was twelve and a half cents.). I think that's the only circumstance under which US currency went to the 1/2 cent, though, because I'm pretty sure there's never been such a thing as a US ha'penny.

Mexico did the same thing with the peso about ten years ago - a New Peso was worth a hundred of the old, but both denominations were still in use (and may still be, I haven't been back in a while).

Like New Coke.

Well, this one caught on, so not exactly the same.

a New Peso was worth a hundred of the old, but both denominations were still in use

A New Shekel is worth 1,000 Shekels, and this is the only currency used. However, many elderly people still, to this day, 'think' in the former-former coin, the Lira.

Oh, and there was once a bill of 10 NIS (now the bill with the smallest currency is of 20 NIS, there are only coins for lower values), and it had a picture of Golda Meir imprinted on it. It was called, for years, until the bill was out of use, "Golda", after her (people would say 'Do you have a change from a Golda?' and 'It costs two Goldas').

"Two bits" comes from the Spanish dolares (doubloons), which were big fat silver coins (of fairly reliable purity) that were easily cut into halfs, quarters, and eighths -- if an eighth was 'a bit' then a quarter was 'two bits.'

(One time when I was at Old Sturbridge Village, the "banker" on duty was an old coin buff who hauled out all the demo coins to show how this worked.)

I'm pretty sure "bits" came from cutting an old Spanish dollar into eight pieces. Which is why eight bits are a dollar. All the proverbs I know with bits in them always have them in even multiples anyway; "Putting your two bits in", as well as "Two bits, four bitx, six bits, a dollar".

[X-post with Theodosia]

Mmmmm...Old Sturbridge Village.

t /Homer

(Edited to add fake tag, which didn't add the first time.)

However, many elderly people still, to this day, 'think' in the former-former coin, the Lira.

I ran across a number of supremely crotchety older folk in France who would count in old Francs, but only when they were complaining about prices -- i.e., "I can't believe they can get away with charging 100,000 a month for this apartment!" If they got a bargain it was always in new Francs.

The latest coinage of guineas took place in 1813; the sovereign, of the value of 20s., was first issued in 1817.

HUH. A sovereign is a pound, then. Learn something new...

The U.S. definitely minted half-cents. [link]