ssh -X does not work on Yosemite

Can no longer use X11 with ssh. Have XQuartz2.7.7 installed. Logging in with X11 via ssh gives the warnings

Warning: untrusted X11 forwarding setup failed: xauth key data not generated Warning: No xauth data; using fake authentication data for X11 forwarding.

In my own system, echo $DISPLAY gives

/private/tmp/com.apple.launchd.GuewxwWwKS/org.macosforge.xquartz:0

However, when I try xauth generate $DISPLAY . trusted, I get the error

xauth: (argv):1: bad display name "/private/tmp/com.apple.launchd.GuewxwWwKS/org.macosforge.xquartz:0" in "add" command

Any ideas in how to fix this?