Try using the following command:
ls -alhrt /dev/* | tail -n 30
looking date-wise, you can get the result of name of the usb devices. For me, following output was produced:
lrwxrwxrwx 1 root root 7 Apr 29 03:26 1:2 -> ../ram2
lrwxrwxrwx 1 root root 8 Apr 29 03:26 1:14 -> ../ram14
lrwxrwxrwx 1 root root 8 Apr 29 03:26 7:0 -> ../loop0
lrwxrwxrwx 1 root root 7 Apr 29 03:26 1:3 -> ../ram3
lrwxrwxrwx 1 root root 8 Apr 29 03:26 1:15 -> ../ram15
lrwxrwxrwx 1 root root 8 Apr 29 03:26 7:2 -> ../loop2
lrwxrwxrwx 1 root root 8 Apr 29 03:26 1:11 -> ../ram11
lrwxrwxrwx 1 root root 8 Apr 29 03:26 1:10 -> ../ram10
lrwxrwxrwx 1 root root 8 Apr 29 03:26 7:5 -> ../loop5
lrwxrwxrwx 1 root root 7 Apr 29 03:26 1:8 -> ../ram8
lrwxrwxrwx 1 root root 7 Apr 29 03:26 1:9 -> ../ram9
lrwxrwxrwx 1 root root 7 Apr 29 03:26 1:7 -> ../ram7
lrwxrwxrwx 1 root root 7 Apr 29 03:26 1:5 -> ../ram5
lrwxrwxrwx 1 root root 8 Apr 29 03:26 7:4 -> ../loop4
lrwxrwxrwx 1 root root 7 Apr 29 03:26 1:4 -> ../ram4
lrwxrwxrwx 1 root root 7 Apr 29 03:26 1:6 -> ../ram6
lrwxrwxrwx 1 root root 8 Apr 29 03:26 7:7 -> ../loop7
lrwxrwxrwx 1 root root 8 Apr 29 03:26 7:6 -> ../loop6
lrwxrwxrwx 1 root root 6 Apr 29 03:26 8:0 -> ../sda
lrwxrwxrwx 1 root root 7 Apr 29 03:26 8:9 -> ../sda9
lrwxrwxrwx 1 root root 7 Apr 29 03:26 8:2 -> ../sda2
lrwxrwxrwx 1 root root 7 Apr 29 03:26 8:4 -> ../sda4
lrwxrwxrwx 1 root root 7 Apr 29 03:26 8:6 -> ../sda6
lrwxrwxrwx 1 root root 7 Apr 29 03:26 8:3 -> ../sda3
lrwxrwxrwx 1 root root 7 Apr 29 03:26 8:7 -> ../sda7
lrwxrwxrwx 1 root root 7 Apr 29 03:26 8:8 -> ../sda8
lrwxrwxrwx 1 root root 7 Apr 29 03:26 8:5 -> ../sda5
lrwxrwxrwx 1 root root 7 Apr 29 03:26 8:1 -> ../sda1
drwxr-xr-x 16 root root 4.2K Apr 29 03:26 ..
drwxr-xr-x 2 root root 720 Apr 29 2012 .
from there, get the name of the usb device, let's for the time sake call it "usbdev".
Then enter the following command to mount it.
mount -t ext3 /dev/usbdev /media/USB_Bkup
sudo mount /dev/sg1 /mnt/