FIG. 1 is a perspective view of a first embodiment of an ornamental design for a shelf unit showing our new design;
FIG. 2 is a front orthographic view thereof;
FIG. 3 is a top orthographic view thereof;
FIG. 4 is a left side orthographic view thereof, the right side orthographic view being a mirror image;
FIG. 5 is a perspective view thereof, showing the claimed design in combination with environmental subject matter, including a mirror unit and a second shelf unit; and,
FIG. 6 is a perspective view of a second embodiment of our design, which is identical to the first embodiment except that the shelves are non-transparent.
The broken line showing of the feet, mitered corners, and the additional structure shown in FIG. 5 is included for the purpose of illustrating environmental elements only and form no part of the claimed design.