Confusion About Ammonite Anatomy Terms

there are a few ammonite shell anatomy terms that have been confusing me.

what do the terms "whorl" and "volution" mean? are they the same thing? are they a full revolution shell growth (360 degrees?) around the unbilical axis? or just 3/4 (270 degrees?) around it?
really? i remember reading somewhere that a volution was 3/4 of a complete revolution (supposedly because the final quarter of the revolution was larger than each previous quarter).

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