Shelf structure
FIG. 1 is a perspective view of a shelf structure, showing our new design, the broken lines are for environmental purposes only and form no part of the claimed design; 
     FIG. 2 is a face view from the right, or from the left, of FIG. 1; 
     FIG. 3 is a side view; 
     FIG. 4 is a top view; and, 
     FIG. 5 is a bottom view.