The map legend or key for each layer is available in the Layer Switcher....
To access the Layer Switcher (to turn layers on or off, display the legend/key, reorder or change the transparency of layers) select the layer icon on the left hand side.
To view the map legend/key of each layer, select the symbol on the right hand side of each layer.
The symbol changes to and the legend/key is displayed.
To hide the legend again click on the symbol.