MicroSD Cards with the use of an SD Card Adapter SDXC Memory Cards (Through an update, SDXC cards up to 128GB are now compatible to the 3DS provided it is somehow formatted to fat32 which it ...

Safely ejecting SD cards and USB flash drives is standard practice to avoid potential data loss - at least on the surface, that is.

MicroSD cards are usually sold with an SD card adapter that fits into a standard reader. This option requires you to open the back of the New 3DS to take out the microSD card.