Art:
 
The family Ovulidae (Cyphoma and Simnia) comes to mind as smoothies who
don't burrow.  Apparently the mantle which covers the shell (which is why
smoothies are smooth in the first place) is for camouflage on sea whips
rather than sand-moving like the moon snails and marginellas, to name
other smoothie groups.
 
The closest thing to an exception the other way (burrowing spinys), that I
can think of, is the pen shell, Atrina rigida, that spends its whole life
burrowed and anchored into the sediment.
 
The exceptions nature makes to her own rules are always amazing.
 
Larry Eaton
Raleigh, NC
 
MR ART WEIL wrote:
 
>      We strike again.
>       This is certain to sound obvious. But I have not seen it
> discussed. It seems that smooth, streamlined shells (Olives, Cowries,
> etc.) are more apt to spend a good part of their lives submerged
> under a layer of mud or sand than are shells with stickers on them (M.
>  pecten, Lambis, etc.) Smoothies can submerge easier. Stickers allow
> for more protection out in the open.
>     So the question is: are there exceptions to this phenomenon?
>        Art