Martin,
 
I'm no cone expert but I looked up your confusing shell in Walls just
for the heck of it.  He calls C. terminus a valid species, differing
from C. gubernator in shape, color and pattern.  C. terminus is
cylindrical rather than conical (C. gubernator) and has the greatest
width below the shoulder rather than at the shoulder (C. gubernator).
It also has strong violet tones, bright reddish tan spire markings where
C. gubernator seems to have more scattered markings of dark brown with
more evident banding and dark brown markings on the spire.  From the
pictures in Walls they look very different and the shape is a dead give
away.  Your C. terminus should have a shape like C. striatus whereas C.
gubernator has a more standard cone shape.
 
Tom Eichhorst in New Mexico, USA