Plural of Darius, Darii?
Catc+us = Cact+i
So
Dari+us = Dari+i
Catc+us = Cact+i
So
Dari+us = Dari+i
The plural form of Darius is "Cancer" because just one is enough.
Fun fact, the english plural form of cactus is actually cactuses. Cacti is the latin plural.