The module positions available depend on the type of menu selected in the style tab.
The type of menu is selected in the style tab in the template administration.
In addition to tthe modules displayed above there is a module position called notallowed. The notallowed module is displayed on galleries that are not accessible to the current user - eg a locked gallery for a user who is not currently logged in.
There are also positions available within each gallery layout. They are called gallery-top and gallery-bottom.
Dedicated positions for Home layouts
Each home layout also has the equivalent above-home and below-home module positions.