The recent mention of the carrier shell Xenophora mekranensis konoi
Habe raises some interesting questions.  The name konoi apparently
indicates that this shell is a subspecies of Xenophora mekranensis.
However, X. mekranensis is an extinct form, known only from fossils.
A couple of weeks back there was a Conch-L discussion concerning the
question whether subspecies necessarily have to be geographically
isolated, and the prevailing opinion seemed to be that they do.
However, the above example appears to be a case where subspecies are
isolated not geographically but temporally.  Are there any ICZN rules
governing such situations?  Is this a common practice?  Would it be
reasonable to say that many recent fossil forms which resemble extant
forms should  be described as subspecies, rather than distinct
species?  Does the nominate species have to be the "older" (extinct)
form (as in the case above)?  What if the living form is named first?
 Can a fossil form that preceded it be named as a subspecies of an
extant species?
Paul M.
Rhode Island