I believe that Alcithoe ostenfeldi is a valid species.

A couple of synonyms of the variable Alcithoe arabica are
unfortunately still in circulation, depressa and swainsoni. These
names are NOT valid. There are no "forms" of A. arabica; the species
is extremely variable, even within a single population; the shell can
lack any nodes at all, or have any degree of development up to quite
large shoulder spines and spire-height also varies. Color varies from
white to flesh and usually has some brown zigzags, but these can be
very weak or absent. Columellar plaits vary in number from about 4 to
over 7. The species goes back to the middle Pliocene and some of the
many named fossil "species" may really be synonyms. Southern
specimens can reach well over 20cm, possibly to 28cm in length.

A. calva is apparently a valid species, not a synonym of A. arabica;
the differences in shell characters, I am told, are subtle (mainly in
the depth of the siphonal notch).

--
Andrew Grebneff
Dunedin, New Zealand
Fossil preparator
Mollusc, Toyota & VW van nut
Temporarily in Calgary, AB, Canada

----------------------------------------------------------------------
[log in to unmask] - a forum for informal discussions on molluscs
To leave this list, click on the following web link:
http://listserv.uga.edu/cgi-bin/wa?SUBED1=conch-l&A=1
Type your email address and name in the appropriate box and
click leave the list.
----------------------------------------------------------------------