Adapical surface (top)
Adoral surface (underside or bottom)
This is an interesting fossil in that it has features from several different types of echinoids that I have seen. It's an irregular urchin since it is not round shaped and it's fairly flat like a sand dollar. Also, the test (skeleton) has both large and small tubercles which is where the spines would attach.
Thanks to my friend Jenaro for this fossil.