I was excited when my friend Nathan gave me this piece of Pachyphyllum woodmani from the Lime Creek Formation near Rockford, Iowa. It's a favorite coral of mine and I've been wanting one for a while. Pachyphyllum is a colonial rugose coral that is different from other rugose corals in that it does not build walls to protect and support it's body. Instead the calyx (cup) is everted (a structure turned from the inside out) into a shallow cup within which can be found the expected septa but they are also present outside of this cup. I'm still looking for more information on this group of fossil corals but this is somewhat typical of the family Phillipastreidae.
Thanks to Nathan for giving me fossils.