The ornamental design for a rearportion of an automobile, as shown and described.
FIG. 1 is a rear perspective view of the rear portion of an automobile of our new design;
FIG. 2 is a front perspective view thereof;
FIG. 3 is a right side view thereof, the left side view being a mirror image thereof, with the exception of the fuel door which is not present on the left side;
FIG. 4 is a front view thereof;
FIG. 5 is a rear view thereof; and,
FIG. 6 is a top plan view thereof.
The bottom view of the rear portion of the automobile forms no part of the claimed design. The lighter contrast portion of the automobile in the photographs is shown to illustrate environment and forms no part of the claimed design.