entirely limited by alisphenoid, the petrosal delimiting the narrow posterior end. No contact between premolars, either upper or lower; molars small and delicate, with poorly developed ectoflexi on M1 but well-developed on M3M4.External measurements in mm of the holotype (and range of three paratypes): HBL 126 (93149), LT 42.5 (3952), HF 15.5 (1415), E 10 (1214); W 10.25 g.Monodelphis gardneri, Pampa Hermosa River, San Ramon, PeruMonodelphis gardneri, Villa Rica-Oxapampa road, Pasco, PeruMonodelphis gardneri, Vilcabamba, PeruDescription.Monodelphis gardneri is a small species (HBL , 150 mm), with short dorsal fur (4 mm); Prout Brown to Mummy Brown, grizzled in dorsal view, three conspicuous blackish dorsal stripes (Fig. 3). Median stripe reaching from between ears to base of tail, widest at mid-back; lateral stripes equally evident, but shorter, extending from shoulders to base of tail. Rump tinged rufous in most specimens, but not conspicuously so (rufous expression may be age related). Rhinarium lackish; pinnae sparsely covered by fine short hairs, appearing macroscopically naked, dark brown, blackish in juvenile. Underparts are Brussels Brown in adults, but Mummy Brown in juveniles; no evidence of throat gland. Tail slightly shorter than half of the head-and-body length; but relatively longer than in similar species (see Comparisons); only slightly paler ventrally; well covered by dense and dark scale-hairs. Dorsal surface of manus and pes well furred, but fingers and toes may appear naked at first glance.Skull small, braincase globular and not flattened (Fig. 4). Inter- and post-orbital constrictions are evident (Fig. 4a). Braincase lacking parietal ridges or sagittal crest. Anterior projection of premaxillae without rostral process. Posterodorsal projection of premaxillae elongated, interposed between maxilla and nasal, reaching the root of P1; infraorbital foramen dorsal to M1 (Fig. 4c). Maxillopalatine fenestrae elongated, from posterior border of P3 to level of M3 protocone, posterolateral palatal foramina small (Fig. 4b). Alisphenoid portion of bulla well inflated, with anterior elongated projection or alisphenoid strut (Fig. 4b) forming a secondary foramen ovale (see Voss & Jansa 2003, Fig. 8c); (primary) foramen ovale almost entirely limited by alisphenoid, the petrosal delimiting the narrow posterior end (Fig. 4b). Basioccipital short, wide, its anterolateral suture with petrosal a raised crest. Crowns of I2, I3, I4, and I5 increasing in width from front to back; anterior cusps present on P1 and P2; no contact between C1, P1, and P2 (Fig. 4c). Small gaps present between lower premolars. Molars small and delicate, poorly developed ectoflexi on M1 but well-developed on M3M4.Comparisons.Monodelphis gardneri is somewhat smaller than sympatric. peruviana in every external and craniodental measurement but larger than M. osgoodi. Compared to similar looking species, it is smaller than M. americana or M. theresa, except in least interorbital breadth (Table 1) but larger than M. iheringi (measurements reported by Gomes 1991); on average, the tail of M. gardneri is relatively longer although shorter in absolute length (Table 1). Monodelphis americana exhibits a longer, wider, and more defined medial stripe that reaches the top of the head (sometimes to the tip of the nose), a condition that is never present in M. gardneri or M. theresa. Because of the mistaken use of