FIG. 1 is a front view of a flat toner cartridge in accordance with the new design;

FIG. 2 is a rear view thereof;

FIG. 3 is a left view thereof;

FIG. 4 is a right view thereof;

FIG. 5 is a top plan view thereof;

FIG. 6 is a bottom plan view thereof;

FIG. 7 is a perspective view thereof; and,

FIG. 8 is a cross-section view thereof, taken along line 8 — 8 of FIG. 4.

The broken lines depict environmental subject matter only and form no part of the claimed design.