Sphodromys Ameghino 1887 Perimys is an extinct genus of neoepiblemid rodent that lived from the Early to Late Miocene in what is now South America.

Fossils have been found in the Cerro Bandera,[1] Cerro Boleadoras,[2] Ituzaingó, Santa Cruz,[3] and Sarmiento Formations of Argentina,[4] and the Galera,[5] Santa Cruz[6] and Río Frías Formations of Chile.

Perimys can be distinguished from other caviomorphs in having euhypsodont and bilophodont cheek teeth, with the hypoflexus/id being conspicuously broader and filled with more cementum than in Prolagostomus and Pliolagostomus.

[8][9] The following cladogram of the Caviomorpha is based on Busker et al. 2020, showing the position of Perimys.

[8] Bugtimys zafarullahi Phiomys andrewsi Metaphiomys schaubi Prospaniomys priscus Myocastor coypus Proechimys polioplus Eumysops laeviplicatus Kannabateomys amblyonyx Echimys chrysurus Ctenomys australis Plataeomys brevis Pithanotomys columnaris Octomys mimax Octodontomys gliroides Chasichimys bonaerense Chasicomys octodontiforme Acarechimys leucotheae Acarechimys minutus Acaremys murinus Galileomys antelucanus Galileomys baios Steiromys detentus Eosteiromys homogenidens Dasyprocta azarae Eoviscaccia frassinettii Eoviscaccia boliviana Garridomys curunuquem Incamys bolivianus Asteromys bolivianus Asteromys punctus Cephalomys ceciae Cephalomyopsis hypselodontus Litodontomys chubutensis Cephalomys arcidens Scotamys antiquus Perimys intermedius Lagostomus maximus Lagidium viscacia Chinchilla chinchilla Banderomys leanzai Soriamys ganganensis Soriamys gaimanensis Luantus propheticus Guiomys unica Microcavia australis Cavia aperea Galea musteloides Dolichotis patagonum