Reference the latest edition of Millard's Classification of Mollusca, I have received the following info:

The new edition has several significant
improvements over the first edition. The following is a direct quote from Millard in
a letter to a gentleman who distributes this work:

 "The first edition just had a list of generic and supra
generic names listed with synonyms and homonyms listed below each and
actually went so far as the Sub Genus level. After a few comments from
various quarters it was decided to make the book a little more user friendly
and fossil genera were added. The format is now that the listings go down as
far as genus level and all generic appellations are in the form of a genus
but in the listing below each genus thee is an audit trail which indicates
with which genus the subgenus was associated. It also contains all the
synonyms and homonyms with the people who regarded them in that line. In
addition there is a range indication for the genus as well as the Type genus
and the Fossil or extant record for the genus. This is a task that has not
been completed as the details are dificult to find and they will be updated
as time allows for further updates."

I hope this answer to my own question is of interest to some of you.

Regards,

Scott Jordan