The largest known member of the mammalian order Multituberculata is the taeniolabidid Taeniolabis, which is known from Puercan (early Paleocene) localities in northern New Mexico, Utah, Montana, and southern Saskatchewan. A locality in the Ludlow Formation of southeastern Montana has produced remains of a new species, T. lamberti n. sp., which is based on a well-preserved dentary with teeth. Isolated teeth from the Tullock Formation of northeastern Montana are referred to T. lamberti n. sp. and Taeniolabis sp.Taeniolabis triserialis, known exclusively from the San Juan Basin, New Mexico, is shown to be a junior synonym of T. taoensis. Taeniolabis sulcatus, the type species of the genus, is recognized as a nomen dubium and is synonymized with T. taoensis based on general morphology and occurrence in the same stratigraphic unit and collecting area (lower part of the Nacimiento Formation, San Juan Basin, New Mexico). The name T. taoensis is retained for this taxon in the interest of nomenclatorial stability. These synonymies limit to one the number of species of Taeniolabis recognized in the San Juan Basin, New Mexico. It is proposed that T. taoensis be designated the new type species of the genus Taeniolabis.
