Abstract Isolated teeth representing several taxa of metatherian mammals were recovered from NMMNH locality L-4005 in the Naashoibito Member, Kirtland Formation, San Juan Basin, northwestern New Mexico. These include fragments of upper and lower molars and a fragmentary premolar that are referred to indeterminate “pediomyids,” an isolated p2 or p3 that is referred to an indeterminate peradectid, and two lower molars, an m1 or m2 and an m4 that are referable to the hatcheriforme metatherian Glasbius cf. G. intricatus. Two upper molar fragments are also tentatively referred to Glasbius. These taxa are part of the Alamo Wash local fauna. Glasbius has been proposed as a potential first appearance datum for the Lancian North American Land Mammal ‘age’ (NALMA). The presence of both Glasbius and the multituberculate Essonodon within the Naashoibito Member support an age correlative with other formations producing Lancian faunas. A Lancian age for the Naashoibito Member suggests that there is a significant discon...