15 letters Mental eccentricity ... as suggested visually by some of this grid's black squares Answer: BATSINTHEBELFRY
15 letters Thing that may appear to be symmetrical but isn't ... like this puzzle's grid Answer: OPTICALILLUSION
15 letters Lyric in the song named by the starts and ends of 19-, 27-, 45- and 53-Across Answer: ITSAHELLUVATOWN