The ornamental design for a petwastebag with mouth, as shown and described.
FIG. 1 is a left side view of my new pet waste bag with mouth design;
FIG. 2 is a right side view thereof;
FIG. 3 is a front view thereof;
FIG. 4 is a rear view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof;
FIG. 7 is a perspective view thereof; and,
FIG. 8 is another perspective view thereof, but shown in a configuration of use for clarity of illustration.
The broken lines illustrate portions of the pet waste bag with mouth that form no part of the claimed design. The broken lines showing the arm in FIG. 8 illustrate environmental structure that forms no par of the claimed design.