"Criterion", "phenomenon", "automaton" and "polyhedron", etc., are borrowings from classical Greek with their plural form ending in "a", as in one automaton but several automata, an interesting phenomenon but unusual phenomena. Because the plural form of these words has the same ending as the singular form of certain nouns borrowed from Latin, such as "alumna" or "formula", and other Greek words from a different declension, such as "dilemma" and "enigma", it is sometimes mistakenly assumed that criteria, phenomena, automata, etc, are in fact singular nouns. This was the case in today's Globe and Mail:
Bilingualism is listed as a criteria of the job.
This should read:
Bilingualism is listed as a criterion of the job.