The spiny-rats included in the genus _Proechimys_ are common in almost
every forest of South America above the Tropic of Capricorn, and in
Central America northward to approximately 12° N, in Nicaragua. In size
and proportions they are similar to the brown rat _Rattus norvegicus_
but actually they belong to a very different suborder of rodents--the
Hystricomorpha. The hystricomorphs are represented in South America by a
large variety of animals, of which capybaras, agoutis and cavies are
common representatives.
The pelage of the spiny-rats has a large number of flattened, spinelike
hairs, especially on the back. The color ranges through different tints
and shades of reddish-brown more or less evenly distributed on the upper
parts; the underparts are usually pure white, sharply contrasting with
the brown color above. The tail is bicolored, brown above and white
below.
The spiny-rats live in forests of different types, generally in the
proximity of water. Shelter is usually procured under boulders, stumps
or masses of roots. The reproductive rate is low; on the average, there
are only two young per litter and only two litters per year.
Sixty-odd names have been given to species and subspecies of
_Proechimys_ in the last hundred and fifty years and no serious revision
of the taxonomy of the genus was undertaken in the last century. The
purpose of the present work is to provide means of understanding species
and subspecies within the genus and to describe the different kinds
known to occur within the confines of Brazil.