Lemurs make up the infraorder Lemuriformes and are members of a class of primates known as prosimians . This type of primate was considered the evolutionary predecessor of simians: monkeys and apes, however this classification is not phylogenetically 'valid'. Three of the four prosimians are in the suborder Strepsirrhini, which is not the same suborder as monkeys and apes, suborder Haplorrhini. The term "lemur" is derived from the Latin word lemures, meaning "spirits of the night," or "ghost(s)" and likely refers to the large, reflective eyes which many of the nocturnal lemur species have. The term is generically used for the members of the four lemuriform families, but it is also the genus of one of the lemuriform species, the Ring-tailed Lemur (Lemur catta). The two so-called flying lemur species are not lemurs, nor are they even primates.