There's a long back-story to this event, but it's not important.
Suffice to say that I removed all the packages from my system, including the shell I like at /usr/pkg/bin/tcsh, and now all my attempts to login are rejected because the shell cannot be found.
Is there a work-around? Thank you -- A test of right and wrong must be the means, one would think, of ascertaining what is right or wrong, and not a consequence of having already ascertained it. J. S. Mill