Hi Brooke,
Well, if your question is a "beginner type question", I am certainly looking
forward to the answers from our Conidae specialists, because after 45 years
of collecting and dealing in shells, I still can't tell these "species"
apart.  I had to laugh last year when a supplier sent me a price list which
included both C. muriculatus and C. floridulus.  I figured I would order some
of each, and perhaps learn something about these confusing species.  Well, he
sent me ten of each, and as far as I am concerned, all 20 are identical.
Jerry Walls, in his classic volume "Cone Shells", lists all three of these
related forms under C. muriculatus, with C. sugillatus as a smooth
(non-granulose) form, and C. floridulus as a high-spired form, with a
somewhat different pattern.  Admittedly, this book is rather dated, which is
why I am anxious to see what some of our resident Coneheads have to say.  But
Walls concludes, "in my opinion, these variants are not worthy of recognition
as they are either insignificant or inconstant".  Everything I have seen
leads me to agree with him, but I am open to other opinions.
Both granules and pustules are raised, rounded projections.  The difference
is size.  Granules are smaller.  A granulose surface feels rough when you rub
your finger over it, like coarse sandpaper.  A pustulose surface feels
"bumpy", but the bumps are larger, and feel smoother.  Granules are actually
just as smooth, but they feel rather sharp, due to their small size (like the
round tip of a ballpoint pen feels sharp).  Nodules (nodulose) are similar,
but still larger.  However, there are no hard and fast rules for separating
these types of sculpture, and also no strict guidelines when it comes to
naming a species, so the name applied to a particular species may or may not
accurately describe it.  Conus granulatus and Calliostoma granulatum are
granulose, but Cypraea granulata and Phalium granulatum are pustulose, while
I would consider Lunella granulata and Strombus granulatus nodulose.
Regards,
Paul M.