Teeth.—Upper molariform teeth with three counterfolds. Lower molariform teeth: premolar with four counterfolds, molars with three counterfolds, sometimes with two folds coalesced in center of tooth.
Comparison.—From P. g. ribeiroi, and P. g. bolivianus, villicauda differs in wider aristiforms. From P. g. ribeiroi, villicauda further differs in: larger and wider incisive foramen; vomerine sheath incomplete or complete instead of always complete and thick. From P. g. bolivianus, villicauda differs in: lower premolars always, instead of rarely, with four counterfolds, and m3 always with three counterfolds instead of usually with only two counterfolds.
Specimens examined.—Total number, 4, from Brazil, Mato Grosso, as follows: Cáceres, Tapirapoã, 3 (MN); Diamantino, Rio Papagaio, Utiarití, 1 (AMNH).
Fig. 62. Proechimys guyannensis villicauda, male, MN no. 1932, Tapirapoã. Type. × 1. × 1.
Fig. 63. Proechimys guyannensis ribeiroi, male, MN no. 1935, Rio Doze de Outubro. Type. × 1.
Fig. 64. Proechimys guyannensis hyleae, male, MCZ no. 30887, Tauarí. Type. × 1.
Fig. 65. Proechimys guyannensis nesiotes, male, CNHM no. 19496, Ilha de Manapirí. Type. × 1.