Here's a breakdown:
* Primates are the order of mammals that includes monkeys, apes, and lemurs.
* Prosimians are a suborder within primates that includes lemurs, lorises, and galagos.
* Monkeys are a parvorder within primates.
* Apes are a family within primates.
So, while ring-tailed lemurs are primates, they are more closely related to apes than to monkeys.