In {HEAD ~ a preferred embodiment} of {TAIL ~ this invention}, the aperture of each of the cooperatively engageable means has substantially the configuration of an isosceles triangle having a vertex in which the respective pivot pin engages in the closed position of the lid member, with the pivot pin moving out of the vertex for accommodating movement of the plate portion from between the edge portions in the course of the movement of the lid member to its opened position 
In { HEAD ~ a preferred embodiment } of { TAIL ~ this invention } , the aperture of each of the cooperatively engageable means has substantially the configuration of an isosceles triangle having a vertex in which the respective pivot pin engages in the closed position of the lid member , with the pivot pin moving out of the vertex for accommodating movement of the plate portion from between the edge portions in the course of the movement of the lid member to its opened position
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