In 1928 when Miller and Allen published their account of "The American bats of the Genera _Myotis_ and _Pizonyx_" (Bull. U. S. Nat. Mus., 144, May 25, 1928) they examined specimens of _Myotis occultus_ which they implied (_op. cit._: 99-100) had only two instead of three premolars on each side of both the upper and lower jaws. In preparing this taxonomic account of bats of the genus _Myotis_, the specimens (type and two from Papayo) of _Pipistrellus cinnamomeus_ seem not to have been examined. Indeed, it is almost certain that they were not examined for the species was renamed; the new name, _Myotis lucifugus fortidens_ Miller and Allen (Bull. U. S. Nat. Mus., 144:54, May 25, 1928), was based on a skull with the corresponding body in alcohol. The characters of this specimen are almost exactly those of _Pipistrellus cinnamomeus_, named and described by Miller 26 years earlier. The type locality (Teapa) of _M. l. fortidens_ is 80 miles westerly from the type locality of _P. cinnamomeus_; both are in the state of Tabasco, and in the same life-zone, at equivalent elevations (neither higher than 50 meters). Since there are no characters of taxonomic worth to distinguish the two named specimens, _Myotis lucifugus fortidens_ Miller and Allen 1928 falls as a synonym of _Pipistrellus cinnamomeus_ Miller 1902. But, according to Miller and Allen (Bull. U. S. Nat. Mus., 144:19, 197), _Vespertilio cinnamomeus_ Wagner 1855 is a name based on _Myotis ruber_ (E. Geoffroy, 1806) from Paraguay and hence _Myotis cinnamomeus_ (Miller) 1902 is a homonym of _Myotis cinnamomeus_ (Wagner) 1855 and is unavailable for the animal from Montecristo when it is transferred to the genus _Myotis_; the species of animal concerned will take the next available name, which seems to be _Myotis lucifugus fortidens_ Miller and Allen 1928. It may reasonably be asked if _Myotis_ and _Pipistrellus_ should be retained as separate genera if the only constant difference between the two is subequal versus unequal upper incisors. In our opinion it would be worth-while for someone who had access to adequate material from both the Old World and the New World to investigate this question. We lack adequate material from the Old World. When Miller and Allen named _M. l. fortidens_ they had only two specimens, the holotype from Teapa, Tabasco, and a referred specimen from Fort Hancock, El Paso County, Texas, approximately 1,200 miles north-northwest of Teapa. We have examined this specimen from Texas (U. S. Nat. Mus., 21083/36121, skin and skull) and regard it as _Myotis lucifugus carissima_ Thomas. Furthermore, we regard the holotype of _Myotis lucifugus fortidens_ Miller and Allen 1928 as specifically distinct from _Myotis lucifugus_ of Miller and Allen 1928. The Cinnamon Myotis, described below, therefore may stand as: ~Myotis fortidens~ Miller and Allen CINNAMON MYOTIS