Thanks Paul!  You have been a real help to me.  I'm going to label these shells as
you suggest (still deciding between C. maculosum and C. stercomuscarum tho').  I
think the Astraea is not the gibberosa, as mine are taller, more like the tecta,
some I'm going to put a tentative A. spirata on them.  Thanks again!  You have
come through where my meager library fails!
Nora

[log in to unmask] wrote:

> Greetings Nora,
> The Donax sounds like Donax punctatostriatus Hanley.  It's the largest West
> Central American species of Donax, and also one of the commonest.  It's
> purple inside, and your comparison to the shape of D. carinatus sounds just
> about perfect.
> The Cerithium could be either C. stercusmuscarum Valenciennes or C. maculosum
> Kiener.  My guess would be C. maculosum, first because I think it looks more
> like C. litteratum than C. stercusmuscarum does, and secondly because it is
> the larger of the two.  C. stercusmuscarum, like C. litteratum, is usually
> about 1 inch, but C. maculosum can reach almost twice that size.  They are
> both common.
> As for the Astraea - There is a little West Central American top shell called
> Astraea spirata (Dall) that is very similar to A. tecta americana.  I don't
> think it is too common though.  If not that, then probably A. gibberosa
> Dillwyn, but that species is usually not as tall-spired as A. tecta americana.
> Regards,
> Paul M.