The Pacas (Agouti genus) are sometimes placed in a separate family Agoutidae or as the subfamily Agoutinae.
Note that the animals commonly known as Agoutis are not the same as those with the scientific name Agouti. Adding to the confusion, the name Agoutis is sometimes used to refer to the whole family Dasyproctidae, including or excluding the Agouti genus. To avoid misunderstandings, some authors refer to the Pacas as the genus Cuniculus.
External link
Dasyproctidae at Johns Hopkins Univ. (http://www.press.jhu.edu/books/walkers_mammals_of_the_world/rodentia/rodentia.dasyproctidae.html)
They are related to guinea pigs and look quite similar, but their legs are elongated.
Confusingly, the related Pacas belong to a genus called Agouti, and are sometimes placed in a separate family called Agoutidae or the subfamily Agoutinae.
To avoid misunderstandings, some authors refer to the Pacas as the genus Cuniculus.