English concertina
English concertina - a type of Concertina
This is the original concertina as invented by Charles Wheatstone. You can recognise one by the 4 parallel rows of buttons and by the supports for thumb and little finger on each end. (There is quite a good picture in Microsoft's Encarta encyclopaedia, except that it is upside down!). The larger baritone and bass English concertinas frequently have wrist straps as well, to help with the greater weight of the instrument.
The two centre rows on each side are in the key of C, the accidentals are distributed between the outside rows. Playing a scale involves alternating between the left and right hands. The layout of buttons is very logical and fully chromatic, and permits very high speeds to be achieved when playing melody (e.g. the Flight of the Bumble Bee, a classic Victorian party piece on the instrument), but is more restrictive if you want to play melody with chordal accompaniment, e.g. ragtime.
Normally the English concertina has 48 keys, but some models had 56. The extra 8 keys are at the high end of the scale and are thus not so useful on the treble, but they can be helpful in tenor-trebles and baritones.