> I've been sorting through my pleurotomaria collection and have been stumped by why they decided
> to break the family name up
> into at least three categories, pleurotomaria, perotrochus and entemnotrochus.... is there an
> easy explanation as to why this
> was instituted and how these families are different. I know there 's  probably a lengthy
> explanation so if it's easier to
> guide me towards a book that would be helpful that to would be most appreciated..........

The Family Pleurotomariidae includes a wide variety of fossil forms, including true Pleurotomaria.
The Treatise on Invertebrate Paleontology, volume I (that is a capital letter i and not Roman
numeral one) Mollusca 1 has a detailed survey of the genera, although the Paleozoic genera have been
extensively reclassified since then.  The modern forms seem to represent distinct lineages from the
late Mesozoic and so are recognized as multiple genera.  Entemnotrochus has a very long slit and an
open umbilicus, and is typically proportionally tall and straight-sided.  Perotrochus and
Mikadotrochus have short slits and closed (Perotrochus) or very narrow (Mikadotrochus) umbilicus,
with Perotrochus typically low and rounded and Mikadotrochus intermediate in height and form.
Height of the slit on the whorl is also important.  There is some variation, though-in the Eocene of
North Carolina we have a low, rounded Entemnotrochus which I will hopefully name soon.  Dr.
Harasewych, at the Smithsonian, was working on a new genus for some of the modern forms but I do not
think it is published yet.

Dr. David Campbell
UNC-CH Geological Sciences
Chapel Hill NC
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