And one of the early. On the surface, one might think that ingenious is somehow based on the word genius. Genius is the correct spelling that comes directly from latin:
大约3分07秒 在这里工作的员工也被 jobs 称为 「genius」(如字幕)。 但是如同高赞所说,这些 genius 受到的是sop的训. My answer always included the qualification that genii is limited to a particular meaning of genius. It is perfectly correct and grammatical.
Genius as a concept (of brilliance, inventiveness, etc.) predates genius as a person (one gifted with genius). If you use the word to mean an intelligent person then the plural can.