The pg_dump -Fd mydb -f mydb.dump command creates a mydb.dump directory with a toc.dat file. The pg_dump man page mentions that pg_restore is able to read this file, but after skimming its man page and stumbling upon this PostgreSQL mailing list thread, I get this cryptic error:
$ pg_restore -l mydb.dump/toc.dat
pg_restore: error: expected format (1) differs from format found in file (3)