The ornamental design for a portion of a motorcycleseat, as shown and described.
FIG. 1 is a perspective view of a portion of a motorcycle seat showing our
new design, the broken lines are shown for illustrative purposes only and
form no part of the claimed design;
FIG. 2 is a top plan view thereof; and,
FIG. 3 is a right side elevational view thereof.
The front, bottom, rear and left side views of the design are not visible
in their normal intended use.