When measuring a snail such as a Lambis, or perhaps something like _Murex pecten_, where spines project past the top of the spire, do you measure from the spire to the anterior end, or from the end to end of the spines (aka the greatest distance)?

 

Also, when measuring sundial shells (acrchitectonicidae, or any flat shell for that matter), do you measure from the apex to the end of the anterior end, or do you measure radially across the shell?

 

~Stephen~