Mystery cylinder

[davemarshall]

I've had this in my collection for so long now, that I can't even remember where it's from or what age it is!
It's cylindrical, with longitudinal ridges covering it, then it narrows in concentric increments.
I have a feeling there's going to be a really obvious answer to this one...

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[davemarshall]

End-on

Attachments:

[brooke]

Looks a bit like the club from the spines of certain echinoids.

[davemarshall]

Yea, I see what you mean, but at 6cm?!