Mesomys is a genus of South American spiny rats in the family Echimyidae.

The genus name Mesomys derives from the two ancient greek words μέσος (mésos), meaning "middle of, between", and μῦς (mûs), meaning "mouse, rat". It refers to the fact that these rodents — literally the "middle mouse" — were considered an intermediate form between the genus Loncheres and the genus Echinomys, both of which are now known to be synonyms of Echimys.

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