I showcased an Ostracod from the Devonian in my previous post and remarked at how small them often are. There are some that can be larger and seen with the naked eye, however, such as this one:
These are from an quarry near Brechin, Ontario in Canada. They quarry Ordovician aged limestone from the Verulam formation which is roughly equivalent to the Lexington formation in Kentucky. For more info on how I came to that conclusion, read this post from the blog "Swimming the Ordovician Seas". Tim did a great job researching and putting together a coherent explanation.
The fossils are 3-4mm in length and were more noticeable, to me, due to my lack of any familiarity with the shape/size/decoration.
A friend from across the border sent me some pictures to use for ID and I think that these are Eoleperditia fabulites. The description remarked that the "...smooth carapaces are rather large... and sometimes mistaken by collectors as the pygidia of illaenid trilobites. The lack of any ornamentation, the shape and long straight hinge like characterize this species."