The Circle Pad Pro is a new accessory for Nintendo 3DS, designed to increase the way the player
enjoys Nintendo 3DS software. It consists of a shell that the Nintendo 3DS slots into with an additional
Circle Pad on the right-hand side (termed "Right Circle Pad" or "Circle Pad (R)") and three shoulder
buttons; these are R Button and the new ZR and ZL Buttons.
XL version for £5.86 http://www.shopto.net/3ds-2ds-ds/3ds/3DSCI02-3ds-xl-circle-pad-pro
Remember these only work for certain games. 11 listed here: http://nintendo3ds.wikia.com/wiki/Circle_Pad_Pro
^Thanks to JC2MULTIPLAYER000