Ross,
 
1.  I just happened to be looking at Petuch's "Atlas of Florida Shells"
the other night and noticed the comment, "Along with C. heilprini, C.
mitchellorum was probably the last-living left-handed cone"(p. 361).
Unfortunately, he does not give stratigraphic details beyond "Pliocene
and Pleistocene" in the subtitle of the Atlas.
 
While I don't agree with a lot of Petuch's species, and he has surely
over-split the subgenus Contraconus, as well, I cannot believe from his
plates that they are _all_ adversarius.
 
2.  Along with ventricosus, a few other species of cone have been found
as sinistral freaks.  There is a picture of a sinistral furvus (claimed
to be truly sinistral and not a printing error) obtained by A.J. da
Motta at Hawaiian Shell News 29(7):5.  The picture has an awkward look
that is more abnormal than would be expected from simply reversing the
plates.
 
I have seen occasional references to the finding of sinistral specimens
in other species of cone, but don't have them readily at hand.
 
3.  Regarding the inheritance of handedness, I recall from my college
genetics class that a sinistral population of Lymnaea stagnalis was
found in Europe and bred with normal dextral snails to determine the
genetics.  The reason this was important is that the handedness of an
individual depended not on _its_ genes, but the genes of its _mother_!
This comes about because, in molluscs, as in some other inverts, the
fate of the embryonic shells is determined at the very first division,
i.e., one of the two daughters is destined to form half "A" of the final
animal, while the other daughter forms half "B."  If you separate the
two daughter cells at this stage, and could raise them both out, you
would get two half-snails.  (This is in contrast to vertebrates,
echinoderms, and some other things, where the fate of the daughter cells
is not fixed until several divisions later.)  Anyway, the direction of
that first division is determined by a cellular structure called the
centriole.  Since spermatozoa contribute little more than the nucleus to
the embryo, the centrioles must, of necessity come from the mother,
hence the strange pattern of inheritance.
 
Bruce Neville
Albuquerque, NM
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