>>Surprisingly, almost all of them (90-95%) were the left valve.  I seem to
>>recall reading an article or study which was conducted on this type of
>>phenomenon but of course cannot remember where I saw it.  Can anyone out
>>there in Conch-land point me to the article or better yet have an
>>explanation.

With left and right valves being mirror images of each other, currents may
transport them differently.  In some cases, if the two valves are extremely
different, one may also be weaker than the other.  Differences in structure
of the valve or assymetric life position may lead to between-valve
variation in predation focus.  If the predator bores through or breaks the
shell, this could lead to preferential weakening and destruction oof one
valve.  In cementing species, the lower valve may be so well attached that
it does not wash up unless the object it attached to washes ashore.  The
first is most relevant for Cyrtopleura.

One attempt at studying this phenomemon in South Carolina around the mid to
late seventies was a spectacular failure.  One side of an isolated inlet
usually had over 90 percent left valves of Dinocardium, the other side had
over 90 percent right valves.  A few hundred of each valve was collected,
painted bright pink, and put in the channel.  Over 90 percent washed out to
sea and were never found again.  Further study eventually had greater
success.  I believe it was published in South Carolina Geologic Notes.



Dr. David Campbell

"Old Seashells"

Department of Geological Sciences
CB 3315 Mitchell Hall
University of North Carolina at Chapel Hill
Chapel Hill NC 27599-3315
USA

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919-962-0685
FAX 919-966-4519

"He had discovered an unknown bivalve, forming a new genus"-E. A. Poe, The
Gold Bug