_Remarks._--As a whole, the samples of the populations of the species do not afford a satisfactory record of the distribution; my concept of the group may be changed when further collections are made in localities geographically intermediate between those from which specimens now are known. If some of the forms prove to be physiologically isolated, they may deserve treatment as full species according to the conventional standards of systematic zoology. _P. panema_, for example, does not seem to be geographically isolated from _P. gratiosus_. _P. denigratus_, at the northernmost known occurrence of the species, actually represents a striking jump in the cline, although collections from intermediate regions may provide intermediate structural stages. Further collecting may also prove that the southern form, _P. iheringi iheringi_, is completely isolated from the rest of the group. However, these samples are certainly more related to each other than any one of them is to that of the other species found in the same range, namely _P. dimidiatus_, and all the forms in question, therefore, seem best arranged as subspecies of one full species. A clinal variation certainly exists among these forms and the most striking differences correspond to larger geographical distances. [Illustration: FIG. 104. _Proechimys iheringi iheringi_, female, MN no. 6453, Ilha de São Sebastião. × 1.] [Illustration: FIG. 105. _Proechimys iheringi bonafidei_, male, MN no. 6183, Fazenda Bõa Fé. Type. × 1.] [Illustration: FIG. 106. _Proechimys iheringi gratiosus_, male, MN no. 4024, Floresta da Caixa Dagua. Type. × 1.] [Illustration: FIG. 107. _Proechimys iheringi panema_, female, MN no. 8288, Campinho. Type. × 1.] [Illustration: FIG. 108. _Proechimys iheringi denigratus_, male, MN no. 8500, Mata do Ribeirão da Fortuna. Type. × 1.] [Illustration: FIG. 109. _Proechimys iheringi paratus_, female, MN no. 4012, Floresta da Capela de São Braz. Type. × 1.] [Illustration: FIG. 110. _Proechimys iheringi iheringi_, female, MN no. 6453, Ilha de São Sebastião. × 1.] [Illustration: FIG. 111. _Proechimys iheringi bonafidei_, male, MN no. 6183, Fazenda Bõa Fé. Type. × 1.] [Illustration: FIG. 112. _Proechimys iheringi gratiosus_, male, MN no. 4024, Floresta da Caixa Dagua. Type. × 1.] [Illustration: FIG. 113. _Proechimys iheringi panema_, female, MN no. 8288, Campinho. Type. × 1.] [Illustration: FIG. 114. _Proechimys iheringi denigratus_, male, MN no. 8500, Mata do Ribeirão da Fortuna. Type. × 1.] [Illustration: FIG. 115. _Proechimys iheringi paratus_, female, MN no. 4012, Floresta da Capela de São Braz. Type. × 1.] [Illustration: FIGS. 116, 117. _Proechimys iheringi iheringi_, female, MN no. 6453, Ilha de São Sebastião. × 1.] [Illustration: FIGS. 118, 119. _Proechimys iheringi bonafidei_, male, MN no. 6183, Fazenda Bõa Fé. Type. × 1.] [Illustration: FIGS. 120, 121. _Proechimys iheringi gratiosus_, male, MN no. 4024, Floresta da Caixa Dagua. Type. × 1.]