I claim the ornamental design for a butterfly back bra, as shown and described.
FIG. 1 is a rear elevational view of a butterfly back bra showing my new design
FIG. 2 is an exploded Rear elevational view thereof showing open
FIG. 3 is an exploded Rear elevational view thereof showing closed
FIG. 4 is a front view thereof
FIG. 5 is a right side elevational view thereof
FIG. 6 is a left side elevational view thereof
FIG. 7 is a top plane view thereof; and,
FIG. 8 is a bottom plane view thereof.
The evenly spaced Broken lines in FIGS. 1-7 are for environmental structure of the article and form no part of the claimed design. The dash dot dash lines within the claimed areas represent stitching in the fabric.