A lemur was an Earth mammal. Patrick Mullen described it as "Sort of a cross between a monkey and a rat." (PROSE: Illegal Alien)
According to The I-Spyder Book of Earth Creatures, the aye-aye was a type of lemur. It was last seen on Earth in 2042 and died out because its habitat was destroyed. However, the last one was kept in the Museum of the Last Ones. (PROSE: The Last Dodo)
The Thraskin were human-sized, lemur-like creatures. They were one of the original inhabitants of Venus. (AUDIO: Voyage to Venus)
Jekylls were small, lemur-like primates native to the planet YT45. (AUDIO: The Mind's Eye)
In 1940, Patrick Mullen misnamed Le Mur Engineering as "Lemur Engineering". The Seventh Doctor thought that this was an odd thing for an English company to call itself and corrected it to "Le Mur", which was French for "Wall". (PROSE: Illegal Alien)