Unable to locate the hard disk icon on the desktop

Hi everybody,
I am using MacBoook Air (model: 4.2) Mac OSX (version: 10.7.5) and it is really amazing.
But, I am having one minor issue. I am not able to locate the hard disk icon on the desktop. I saw it until last week and this week onwards it got disappeared. I tried to see if there are any settings where I can set it to Show the icon. But I couldn't find any settings as well.
How can I make it appear on the desktop? Please kindly advise. Thanks in advance.
