Sometimes news takes a long time to get around!! - In 1990, H. A. Rehder (The
Nautalis 103(4): pp 117 - 123: Clarification of the identity of the snail
Margarites groenlandicus (Gmelin, 1791)) set the record straight on this
species, but for some reason, there is still a LOT of confusion in the
Conchological Community.  If i recall the details correctly, it seems that
someone (can't remember who - anybody know??) got it confounded (ie, switched)
with M. striatus (Leach, 1819) about 100 years ago, in a paper that others used
as a reference.  As a result, M. striatus became little-used, with the name
groenlandicus being commonly used for this species.  Meanwhile, the REAL
groenlandicus became known as umbilicalus Sowerby I, 1829, which was sometimes
recognized as a distinct species, and sometimes placed as a subspecies or
variety of groenlandicus.

SO, for the record, here are the two species:

Margarites striatus Leach, 1819: a boreal/sub-arctic and northern temperate
species, circumboreal, with a few Arctic "outposts" (such as the Axel-Heiburg
Shelf at 81 degrees North in Canada - not published).  It is the species found
in Iceland that Mr. Kirsch has - with distinct spiral groves on the body whorl.
It is the species meant by 99.9 references to "M. groenlandicus Gmelin".

Margarites groenlandicus Gmelin, 1791 is an arctic species (again, circumboreal)
with sub-arctic outposts.  It is very seldom seen in private collections, and
occurs in deeper water than striatus, which gets into the subtidal zone
sometimes. It has a smooth body whorl.

I hope this clears up the confusion, at least amongst the folks who read this posting.

-Ross.