>I guess the real question is why are there not more non-boreal species
>that occur on both sides of the Atlantic?

Ross,

The question that has me baffled is how there are certain very common
shells found in Florida (Busycon species, for instance) that are not found
in the Bahamas -- just 54 miles east. Conversely, Turbinella angulata,
which is a prolific species in the Bahamas, is not found in Florida. While
I have found many Cypraea zebra in the Bahamas, I have never seen a
C. cervus. Has anyone else collected this species in Bahamian waters?

Best regards from chilly (for us) Florida,
Jim

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