Synaptomys

1. cheek teeth with crowns bearing prismatic pattern of dentine
2. M¹ and M² with middle portion divided into a number of sharp-angled triangles
3. cranium abruptly constricted in interorbital region
4. dorsal border of infraorbital foramen virtually straight
5. basal length < 45 mm
6. upper incisors grooved near lateral margin
7. zygomata slightly expanded in middle