Miller mentioned also that it had the "Inner upper incisor distinctly smaller than the outer, not approximately equal to it as is the case in P. subflavus."

At this point it is well to make clear that each of the genera Pipistrellus and Myotis contains a large number of species and that the differences between the two genera are few. Our examination of American specimens reveals only one differential character: In Myotis the outer upper incisor is distinctly larger than the inner, whereas the two incisors are of approximately equal size in Pipistrellus. It may be noted that the outer upper incisor of several, but not all, species of Myotis has a well-developed concave surface directed toward the canine whereas this surface is flat or convex in Pipistrellus. In both features, the type of Pipistrellus cinnamomeus Miller agrees with Myotis and differs from Pipistrellus.

Five years after naming and describing Pipistrellus cinnamomeus, Miller published his monumental work entitled "The families and genera of bats" (Bull. U. S. Nat. Mus., 57, June 29, 1907) wherein he points out the differences in the upper incisors between Pipistrellus and Myotis (by a lapsus plumae ascribes subequal incisors to Myotis and unequal incisors to Pipistrellus) but seemingly failed to reëxamine P. cinnamomeus in the light of this better understanding of the two genera, or if he did examine P. cinnamomeus he possibly was misled still by the absence of the third premolar on each side of both the upper and lower jaw.

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.