“An apostrophe followed by “s” was often used to mark a plural;[4] specifically, the Oxford Companion to the English Language notes that
There was formerly a respectable tradition (17th to 19th centuries) of using the apostrophe for noun plurals, especially in loanwords ending in a vowel (as in … Comma’s are used, Philip Luckcombe, 1771) and in the consonants s, z, ch, sh, (as in waltz’s and cotillions, Washington Irving, 1804)…”