plurality of grooves extending radially outwardly from a central pivot and ends 64 and 64a of panels 65 and 66 comprise the cogs which engage the grooves it should be understood that it is within the contemplation of the invention to include cogs molded to an end of a panel and shaped to engage said grooves in this illustrated configuration the weight of the panel maintains the end or cog of a panel in a groove to resist pivoting movement of the panel movement of a panel upwardly along the pivot axle releases the end from the groove to enable pivoting of the panel about the axle fig4 illustrates elements comprising a retractable cover assembly of the invention mounted to an attachment frame having integral end members and an embodiment of a cog and groove arrangement of the invention retractable cover assembly 50 is illustrated as comprising cylindrical member 51 which is shown as having hollow 52 spring 53 internal spring mount 54 axle spring mount 55 end piece 56 axle frame 57 axle frame mounting clip 58 and flexible cover 59 axle spring mount 55 is fixed to axle frame 57 which in turn is mounted by clip 58 to upper member 80 and extends through end piece 56 centrally into hollow 52 internal spring mount 54 is fixed to cylindrical member 51 and spring 53 extends between internal spring mount 54 and axle spring mount 55 such that rotation of cylindrical member 51 about axle spring mount 55 causes retracting tension loading upon spring 53 the cover is.