Door County Wisconsin fossil

[rbh1515]

I find many Silurian period fossils on our Lake Michigan shore in Door County, Wisconsin.  I’m able to ID most of them.  Found this one today.  Not quite sure what it is?  Any ideas?

[Kane]

My guess would be the cup of a rugose coral.

[Jeffrey P]

Yes. That's view looking down from the top showing the margins of the septa (walls) that divide the coral's interior. Therefore, the horn shape is not visible. Those look especially cool when naturally worn and polished. 

[rbh1515]

Makes sense.  I do have one (bottom left) where you can see the horn shape…it is a much smaller fossil!