A few years ago a member of the Fossil Forum gave me these two blastoids in matrix. What I know about them is that they came from the Alpena area of Michigan and are Devonian in age. I reached out to my friend Joe K. for some ID help and he suggested that it comes from the Thunder Bay formation and would be classified as a Heteroschisma subtrunctatum.
I need to get both specimens cleaned and prepped so that they are more visible. The Thunder Bay formation (or limestone, depending on who you are talking to) is the uppermost layer of the Traverse group in Michigan which places it as latest Givetian stage of the Devonian.