In MacX the command:
creates an xterm window.
/usr/bin/X11/xterm -display "®display -sb -ls -title "®host xterm"
creates a Decwindows xterm window.
/usr/bin/X11/dxterm -display "®display" -sb -ls -title "®host dxterm"
The symbol before display and host in the double quote marks is an R with a circle around it. This is created on the Mac by holding the option key and pressing r.