[PLUG] Can't see files in Virtualbox shared device

[John Jason Jordan]

I need a program that cannot be installed on my ancient Xubuntu 14.04
until I upgrade it to 18.04, which can't happen yet. It will also run
in 17.10, so I Installed a bare 17.10 in Virtualbox. I have it working
and the needed software is installed and running. However, the software
needs data from an SD card. I added the SD card as a shared folder and
it appears in 17.10, but only the device appears, the contents are not
visible in 17.10 in Thunar or the terminal. I also shared ~/, and this
appears, but only the name, none of the files appear.

There is probably a really obvious answer that I'm too dense to think
of.