As has already been said the melody is usually on what would be the tenor line in normal SATB scores. This is not surprising as in "West Gallery" music it is usually the tenor who "holds" the melody - the word tenor comes from the latin verb "to hold".

In most Shape Note / Sacred Harp music however, parts may be sung in any octave so the normal conventions of male voices taking the lower parts and females/boys the higher does not have to be adhered to. In fact having parts sung in two (or even three) octaves adds a richness to the result.