Slow to catch up on emails...
...there are hundreds of pairs of similar molluscan species on either side of the Panamian isthmus.
>  As it happens, the world has another isthmus that separates warm waters:
>  Suez separates the Red and Mediterranean Seas. ;-)  My goodness, I seem to
>  have misplaced my notes. Would someone care to tell us the observations  at
>  this test case and how they compare to the Panamanian situation?

Unfortunately, the strait of Suez was the only connection between the proto-Mediterranean and the rest of the oceans.  When it closed in the late Miocene, the Mediterranean largely dried up-not a good situation for most mollusks.  The strait of Gilbraltar re-opened at the Miocene-Pliocene boundary, so the modern Mediterranean fauna (apart from invaders via the canal) is composed principally of Atlantic-derived invaders.  Sea level variation in the Plio-Pleistocene may have formed some Mediterranean-Red Sea connections, but I don't know enough Palestinian paleogeography to be certain.  I'm pretty sure the Dead Sea region has had marine innundation, but don't remember about the connection over to the Mediterranean.  The rock outcrops in Palestine are mainly Eocene or older, so the Plio-Pleistocene is largely eroded, to the extent it was deposited.  However, that does make easier access to older beds.  There are exceptionally preserved Cretaceous mollusks exposed on the Mount of
Olives-no wonder it was a popular place to visit in Biblical times!  [No Oliva, though.]

    Dr. David Campbell
    Old Seashells
    University of Alabama
    Biodiversity & Systematics
    Dept. Biological Sciences
    Box 870345
    Tuscaloosa, AL  35487-0345 USA
    [log in to unmask]

That is Uncle Joe, taken in the masonic regalia of a Grand Exalted Periwinkle of the Mystic Order of Whelks-P.G. Wodehouse, Romance at Droitgate Spa

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