Shelf

FIG. 1 is a front, top and right-side perspective view of the shelf showing my new design; FIG. 2 is a front elevation view thereof; FIG. 3 is a rear elevation view thereof; FIG. 4 is an enlarged left side elevation view thereof; FIG. 5 is an enlarged right side elevation view thereof; FIG. 6 is a top plan view thereof; FIG. 7 is a bottom plan view thereof; FIG. 8 is a rear, bottom and left-side perspective view thereof; and, FIG. 9 is an enlarged view, of circled portion 9 , of FIG. 6 , thereof. The broken lines throughout the drawing figures depict portions of the shelf that form no part of the claimed design. The dot-dash broken lines depict the boundaries of the FIGS. 6 and 9 enlargement that forms no part of the claimed design.