I am English (i.e. from England). Sadly our definitive
Dictionary's online presence is a charged for service. Presumably this is to
keep speakers of lesser English languages where they belong intellectually ![Smile [:)]](/emoticons/emotion-1.gif)
That being some of the reason the two languages are subtly different
("subtle" itself being a word only proper English speakers would
properly understand, like sarcasm).
Not having the OED to hand, my own British-English (real English, as opposed to
borrowed) dictionary informs me that "geniuses" is correct, unless
speaking about Roman myth, guiding spirits (present at birth and death),
guardian spirits or Arabic myth, in which case "genii" is correct.
Rather amusingly this is the exact definition the "American English"
dictionaries provide at www.dictionary.com.
What is more amusing is the fact that many of you think that Google is a
dictionary and the number of posts about either "Geniuses or Genii"
has some relevance on which to use.
2 minute to research two proper references, Genius!
Not to be confused with Guinness.