The ornamental design for a cuttingblade for a riding mower, as shown and described.
FIG. 1 is a front view of a cutting blade for a riding mower showing our new design;
FIG. 2 is a rear view thereof;
FIG. 3 is a left side view thereof;
FIG. 4 is right side view thereof;
FIG. 5 is a top view thereof;
FIG. 6 is a bottom view thereof;
FIG. 7 is front perspective view thereof;
FIG. 8 is rear perspective view thereof;
FIG. 9 is an enlarged left side view thereof;
FIG. 10 is an enlarged right side view thereof; and,
FIG. 11 is an enlarged perspective view of a portion thereof taken along lines 11-11 in FIG. 7.
The broken line showings of FIGS. 1-11 are environmental only and not part of the claimed design.
The dashed-dotted line showings of FIGS. 1-11 illustrate a boundary between the claimed design and environmental features and form no part of the claimed design.