James,
 
Your unknown cone may be a case of, "If it walks like a duck, quacks like a
duck, and looks like a duck -- it  is a duck."  I have seen Conus retifer
with large white triangles (the illustration in Eisenberg's has them) and
I'll bet they sometimes lack the dark brown banding as mine has much heavier
banding than the one in Abbott and Dance's compendium.  So it may be just a
variation in pattern and color; there are a lot of cases of great variety in
plenty of shell families, cones are right on the top of that list.  Living
where you do you ought to be able to take it to a shell dealer.  Better yet,
join one of the many shell clubs in your area.  I guarantee if you do that
you will find plenty of people in the club who are very knowledgeable about
almost any shell family you become interested in.
 
Tom Eichhorst in New Mexico, USA (one of about seven proud founding members
of the High Desert Shell Club)