In response to Paul M.'s question about the size, the Anachis I collected
ranged between about one quarter and one half of an inch.  I made the mistake
of trying to ID the shells by looking primarily at the smaller shells with
better-defined ribs.  Now that you pointed out that adult A. lafresnayi have
more ribs than A. avara, I am pretty sure that the west coast Florida shells
are lafresnayi and the east coast shell is avara.  However, I'm still not
positive about the shells from S. Padre, TX.  All four are juveniles, and
they have between 12-15 ribs, which makes me think they are A. avara.  Are
both species commonly found in Texas?
Thanks to those who have already responded,
Patrick