Links to the reviews sub-indexes by volume (in http://whitmanarchive.org/criticism/reviews/index.html) were returning 404 errors. I compared the criticism sitemap on the server with my local copy and discovered that the section for handling the sub-indexes had been trimmed pretty drastically. I copied that section from my local sitemap file into the one from the server and re-uploaded. The links now work. The differences between the two sitemap files were much more extensive, but I decided not to simply restore the older file without knowing who made the changes and why.