A new genus and species of podocnemidid pleurodire, Caninemys tridentata, is described on the basis of a skull collected by L.I. Price in 1962 from the late Miocene of Acre, Brazil. It is unique among podocnemidids (and all other turtles) in having greatly inflated maxillae, each with a ventral, toothlike process. Along with a midline process of the premaxillae, these processes form a tridentate condition in the upper triturating surface, also unique among podocnemidids but comparable to the condition in the kinosternid Claudius. This skull has previously been identified as the shell-based genus Stupendemys, but there are no associations supporting this assignment. The type specimens are separated by over 2000 km, and other large podocnemidid taxa are known from this time and region. Although relatively large with a condylobasal skull length of about 17 cm, Caninemys was probably about half the size of Stupendemys. Phylogenetic analysis of 63 skeletal characters provides evidence that this new taxon nests within the family Podocnemididae as follows: (Bauruemys (“Roxochelys” (Podocnemis (Caninemys (Dacquemys ((Erymnochelys, Peltocephalus) (Neochelys (Shweboemys, Stereogenys)))))))).