Both shells are Nerita polita.  Without seeing the operc, it can be very
difficult to separate these species with 100% surety, but there are several
shell structural clues that can help.  Nerita maxima is seldom as glossy or
shiny, usually has definite spiral bands, and has a "bit" more of a spire
(almost flat in N. polita).  The problem is that each of these characters
can vary and I have seen specimens of N. polita and N. maxima that were
almost identical in shell structure and color.  The operc, of course, is
always a telling feature and is 100% diagnostive.  N. polita has the typical
flat surfaced operc while N. maxima has an operc that is covered with
denticals.  If you would like I can send the draft write ups for both
species and the color plates.  Just let me know.

Tom

--------------------------------------------------
From: "Olivier Caro" <[log in to unmask]>
Sent: Tuesday, June 26, 2012 3:06 AM
To: <[log in to unmask]>
Subject:      [CONCH-L] Neritidae question

> @ Tom Eichhorst and other specialists or enthusiasts...
>
> Here are two Neritids from Samoa, dead collected, without operc. I'd
> like to get your opinion regarding their ID, please.
>
> http://www.idscaro.net/sci/03_myst/index.htm#gotosamoa
>
> Thanks!
>
> Olivier Caro
>
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