adverb /sɛ.ɹiˈɑː.tiːm,ˌsɛ.ɹɪˈeɪ.tɪm/
Point by point; taking one topic or subject at a time in an order.
Seriatim, I know of no good Authority that this Adverb can claim, though it has got a Place in our Dictionaries, and School-Books.
Wikipedia foundation.