If anyone can please share their knowledge on what this may be it would be much appreciated! I found it along the bank of the Illinois River in Morris. Image 1 was taken from what I assume to be the top and image 2 is from the bottom. Image 3 is from the side which appears to me to be a crossectional view of the midline of the fossil. It measures approximately 2"W x 2"L x 1"H. I'm a novice collector but my first thought was half of an urchin or something along those lines. Thank you.