Binary descriptions:

xserver-xorg-input-synaptics: Synaptics TouchPad driver for X.Org server
xserver-xorg-input-synaptics-dbg: Synaptics TouchPad driver for X.Org server
xserver-xorg-input-synaptics-dev: Synaptics TouchPad driver for X.Org server (development headers)

Last common version:

1.8.0-1~exp2ubuntu2