It is a very active Bat, flying over farmyards and gardens and about houses, frequently uttering its shrill little squeak as it snaps up the flies and small beetles, pouching and eating them without alighting. It continues its flight all through the night, and has a longer period of activity than any other species, for it leaves its hibernaculum in March and does not retire until winter has begun. Even then, a moderately high midday temperature is sufficient to awaken it and bring it out for an hour's hunt. It is this habit that accounts for the letters in the daily papers from City gentlemen who report the presence of a Bat flying along Cornhill or Cheapside early in January. It is not particular in regard to its sleeping place, and is frequently found under roofs, behind rainwater pipes and gutters, or in any crevices between woodwork and brickwork in buildings. Any regular dormitory acquires a very fetid odour from its use. The dental formula of the Common Bat is: _i 2/3, c 1/1, p 2/2, m 3/3 = 34_. Schreber's name of _Vespertilio pipistrellus_ was bestowed in 1774 and is the oldest name; in the British Museum Catalogue it is _Pipistrellus pipistrellus_, a combination invented by Miller in 1897. *Serotine* (_Vespertilio serotinus_, Schreber). The Serotine and the Noctule are our two largest Bats, and in the early records they were very much confused. Though similar in size, they may be known apart by the shape of the ear; in the present species oval-triangular with the tips rounded. The fur is also of a darker brown, and there are other points of difference, such as the possession of two additional teeth by the Noctule. But for a few records of its occurrence in Essex, it might be said to be restricted in Britain to that portion of England bounded by the river Thames and the English Channel. A few examples have been taken in Cornwall, and other counties in which it is found are Surrey, Hampshire, Sussex, and Kent. It occurs throughout the Isle of Wight--where it is known as Rattle-mouse--but Kent is its British metropolis, where it is the commonest Bat. It extends through Central and South Europe, from Denmark to the Mediterranean and eastward into Asia.