(Excerpts from some Publications Q&A between Dick Petit & Leslie Allen
Crnkovic)

Question 1:
I have always heard that there were 3 volumes to his work.
    If this is Volume 1
        Walter Cernorsky 1967/1971  - Marine Shells of the Pacific, 2nd Ed,
Pacific Publications
    And this is Volume 2
        Walter Cernorsky 1972  - Marine Shells of the Pacific, Volume II,
Pacific Publications
    Is this Volume 3?
        Walter Cernorsky  1978 - Tropical Pacific Marine Shells Ed, Pacific
Publications

Answer 1:
    You are correct on the Cernohorsky titles.  I remember reading somewhere
a long time
    ago the reason why the last one was titled slightly different and is not
specifically  "Vol III"
    but right off all I remember is that the reason didn't make much sense
to me at the time...

Question 2:
Was there ever a part 2, Gastropoda, etc. published for this?
    Verrill & Bush 1898 - Revision of the Deep-water Mollusca of the
Atlantic Coast of North America
    with Descriptions of New Genera & Species, Part I Bivalvia,  Smithsonian
Institute,
    from the Proceedings of the United States National Museum, Vol XX, pp
775-901 # 1139

Answer 2:
    No.  There was never a gastropod sequel or a volume 2 to the Verrill &
Bush
    Revision of the Deep-water Mollusca of the Atlantic Coast of N. A.
Bivalve paper.
    Both of them published numerous papers on gastropods over the years,
    but  nothing that would be a companion to the Bivalve volume.