xmess/xmame usage?

[Juhana Sadeharju <kouhia@nic.funet.fi>]

I have game CD "spectrum classics, 3000 classic games" by Revive.
How to run "hobbit.sna" with xmess, which claims to support
that format and device?
spectrum     cassette    (cass)     .wav
             snapshot    (dump)     .sna  .z80  .sp

Usage: xmess <system> [game] [options]

Trivial first try like "xmess spectrum hobbit.sna" does not work.

I also find it very unfriendly that xmess/xmame turns Gnome
display to complete black. I have go to console (ctrl-alt-1) and
then back (alt-7) to fix the situation. A windowed version would
be nice.

Juhana