A cover for an open-topped receptacle, which receptacle is generally rectangular and has a peripheral prominence. In its preferred embodiment, the cover comprises a substantially planar central web bounded by an integral channel which is generally registrable with the peripheral prominence of the receptacle. The channel is configured to effect nested reception of the peripheral prominence within the channel. The channel has a width and comprises four channel segments and four corners. Each of the corners is established substantially at an intersection of a respective two of the channel segments and each of the corners is truncated at least the width of the channel athwart each of the respective two channel segments intersecting at the corner.