Simon’s spiny-rat is a large rodent with an elongated body, long face and ears, long hind feet, and a long tail. A Peruvian reserve study found only two individuals, both in undisturbed forest.
It has an elongated body, long face and ears, long hind feet, and a long tail. Its back is paler than that of other Proechimys described at the site; the belly is white and the tail is distinctly two-colored.
Its range is described as the western Amazon Basin. At Reserva Nacional Allpahuayo-Mishana in northeastern Peru, the two captured individuals came from undisturbed varillal and clay forest; it was rare at that site.
An extinction-risk assessment has not been added yet.