Tom,
Phil Poland and I went around on this a few months ago.  I can't remember
if the discussion was telecast on Conch-L.  Phil and I were in agreement
with the characters used.
 
N. usnea (reclivata):  basically mainland from FL to Central America.
Freshwater to brackish.  Usually large, round or elevated spire.
Greenish-black with fine balck axial lines, NEVER with chevrons.
 
N. piratica: S. Mexico to northern South America.  Freshwater to brackish.
Basically the southern usnea.  Usually a little rounder.  Axial lines
coalesce to form a net-like pattern, NEVER light colored chevrons.
 
N. clenchi:  Antilles.  Freshwater only.  Usually rounded, lighter (in
weight) than virginea.  Whitish spots and/or chevrons.  Other characters
mentioned by others don't work.  This is really a gessalt thing, but once
you get it, it's like riding a bicycle.  You can pick one clenchi out of a
thousand virginea. NOT in Florida.
 
N. virginea: Florida and Antilles.  Brackish to fairly marine.  Thick,
dense, marble-like shell, usually elevated spire.  Endless variety of
lines, chevrons, spots, colors.
 
Don't forget N. zebra and N. latissimus (or is that the Panamic thing?).
The former, southern Antilles to northern South America, large, broad axial
zig-zaggy lines, looks "Indo-Pacific".  Properly ID'd specimens VERY rare
in collections and with dealers.  Freshwater.
 
The latter is easy, thin shelled, broadly expanded, flaring lip,
greenish-brown with axial lines and dots. Freshwater of the Antilles and I
think Central America.
 
Refer to Russell, 1941 (?) for review of the Neritidae of the Western
Atlantic.  He's the only one who has treated this group with the proper
respect.  After nearly 20 years of looking at these neat little baubles
(nerites were my first love and still remain high on my list), I have found
just about everything he said to be right on the money.  Too bad he wasn't
foolish enough to tackle the Indo-Pacific fauna!
 
Hugs,
 
Kurt
 
At 08:39 AM 9/28/98 -0400, you wrote:
>Can anyone give me a good way to differentiate Neritina usnea [=reclivata],
>N. clenchi, and N. virginea? Where does N. piratica fit in? The
>characteristics in Abbott (1974) don't seem to hold up to inspection. Also,
>does anyone know of a freshwater Neritina from Montserrat, or literature
>that may help?
>
>*  G Thomas Watters               *
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