base rings 2 by means of peripheral portions 5 of increased flexibility ensures that the depression of a shell 4 into its inverted position is not followed by the shell 4 reverting under its own elasticity to its original position similarly the linking of the tip portions 6 of the shells 4 to the wall portions thereof by means of peripheral portions 7 of increased flexibility also ensures more complete inversion the marker board as shown and which in this example can be used for playing simple games with well known rules can suitably be formed of flexible plastics or synthetics or natural rubbers in such cases it need only be ensured that the shells 4 are of increased flexibility as compared with the frame portion 1 the board as shown can be appropriately formed as a single element by means of an injection or compression molding technique and suitable materials can for example consist of ethylene vinyl acetate plasticized p v c polyurethane and natural and synthetic rubbers fig4 and 5 of the drawings show how the board can be formed of a three component two material system as seen in these figures the shells can be preformed in a sheet 11 of a highly flexible material such as for example latex and this sheet 11 with the preformed shells is.