How to Eject USB Devices and Memory Cards in OS X
Macs are all about a beautiful, streamlined aesthetic, and a big eject button on the keyboard or side of the system (for those with optical drives) would ruin its sleek design. Instead, Macs have their own process.
1. Click on the Finder icon at the bottom left of the screen (the left most icon on the Dock).
2. Eject external hard drives, memory cards and more by clicking on the Eject icon next to the name of the device in the Finder window. Look on the left side.
3. Drag the device to the Trash on the desktop to eject it, as an alternative.