The plural for series and the singular for series are the same - simply "series."
The plural form of series is series.
The noun 'series' is the plural form of an uncountable (mass) noun. singular: A series of playoffs took place before the tournament. plural: He has published three series of adventure novels, each with a different hero.
series
The noun series is spelled the same for the singular and plural; one series, two series.
It depends on whether you are using the word series (pl series) in the singular or plural, e.g. there were ten series (plural) of 'Friends'; I enjoyed series one (singular) the most
Seris is the plural form of Seri
Series means a collection of books, events, etc. so it is plural automatically.
Series is plural, though often times used to describe what is thought of a singular event.
Series is a noun that has the same form in the singular and the plural. There is no need for an apostrophe, unless it is in the possessive case: series's for the singular possessive and series' for the plural possessive.
it's the same
species, series
The form 'series' is both singular and plural; for example: I've scheduled the week off from work to attend the series of chess tournaments. I have all five series of prints and I'll subscribe for the new one when it's available.