Twenty-fourmo n. A book composed of sheets, each of which is folded into twenty-four leaves; hence, indicating more or less definitely a size of book whose sheets are so folded; usually written 24mo, or 24°.
... with pre-Columbian America; yet one of the most interesting of all book forms was current in Mexico before the Conquest. As in the case of the Chinese book, it looks superficially like ours; we think it is a tiny quarto until we see that its measure is rather that of an oblong twenty-fourmo; that is, its dimensions are just scant of five inches high and six inches wide. It has thin wooden covers and is, over all, an inch thick; but between these covers is a strip of deerskin twenty-nine feet long ... — The Booklover and His Books • Harry Lyman Koopman
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