The ornamental design for a long-bristled brush, as shown and described.
FIG. 1 is a front-top-left perspective view of a long-bristled brush showing my new design;
FIG. 2 is a front-top-right perspective view of a long-bristled brush showing my new design;
FIG. 3 is a front-plan view thereof;
FIG. 4 is a back-plan view thereof;
FIG. 5 is a left elevation view thereof;
FIG. 6 is a right elevation view thereof;
FIG. 7 is a top plan view thereof; and,
FIG. 8 is a bottom plan view thereof.
The broken line showing the bristles in FIGS. 1-8 are included for the purpose of showing environmental structure and form no part of the claimed design.