1829. _Pipistrellus_ Kaup, Skizzirte Entw.-Gesch. u. natuerl. Syst. europ. Thierw., Vol. 1, p. 98, Type, _Vespertilio pipistrellus_ Schreber (not seen by us, after Miller, N. Amer. Fauna, 13:87, 1897). _Range in the New World._--In North America from southern Canada to Honduras (47 degrees to 5 degrees North Latitude) and from the Atlantic to the Pacific; not recorded from the West Indies or South America. _Characters._--Size small; tail approximately as long as outstretched leg; ears well developed with prominent tragus; dental formula: i.2/3; c.1/1; p.2/2; m.3/3; two upper incisors subequal and outer one lacking a concavity on surface facing canine; dentition otherwise essentially as in _Myotis_ Kaup except that third premolar is always, instead of rarely, absent. _Remarks._--There are two species in North America. Their geographic ranges, as now known, meet, but do not overlap. Certain differences between the two species are listed in the parallel columns below. Most of these differences in the skull and teeth are illustrated in figures 22 and 23 on page 92 of Miller's "Revision of the North American bats of the family Vespertilionidae (N. Amer. Fauna, 13, 1897)." ====================================================================== Structure | _P. hesperus_ | _P. subflavus_ ====================================================================== Color | Predominately gray | Predominately brown --------------------+-------------------------+----------------------- Foot | Less than half as long | More than half as long | as tibia | as tibia --------------------+-------------------------+----------------------- Thumb, length of | Less than 4.9 mm. | More than 4.9 mm. --------------------+-------------------------+----------------------- Tragus | Blunt, terminal part | Narrow, straight | bent forward | --------------------+-------------------------+----------------------- Skull | Nearly straight | Dish-faced (dorsal profile) | | --------------------+-------------------------+----------------------- Braincase | Small | Large (viewed from above) | | --------------------+-------------------------+----------------------- Palate | Extending far behind | Extending short | molars; spine short, | distance behind | | molars; spine long, | narrow at base | wide at base --------------------+-------------------------+----------------------- I2 | Unicuspidate | Bicuspidate --------------------+-------------------------+----------------------- I3 | Accessory cusp present | Accessory cusp absent