SPECIATION 311
Subgeneric variation 312
Specific variation in the subgenus _Proechimys_ 314
Subspecific variation in the subgenus _Proechimys_ 317
Specific variation in the subgenus _Trinomys_ 320
Subspecific variation in the subgenus _Trinomys_ 322
TAXONOMIC CHARACTERS 323
Size and proportions of external parts 323
Pelage 324
Skull 326
Incisive foramen 326
Teeth 327