Catalog Number: CG-0090
This gastropod has a highly probable Identification. I have confirmation that Trepospira sphaerulata is found in this and nearby limestone layers. Based on the nodes visible on the top of the last whorl, a local fossil gastropod expert gives this as a likely identification. This specimen comes from the Pine Creek Limestone locality which has been the source material for many of my recent posts.
The only fact keeping me from being sure is the lack of suture ornamentation. These should display as regular raised nodes. However, the fact that this is a very flat, wide shell helps. The spire is visible as small and only raised in the very center.
Example showing ornamentation from the late 1800’s
The example below was regarded as a perfect specimen. The suture ornamentation is very apparent.
Additional Photos of CG-0090
Specimen CG-0090 
Underside of specimen. 
The tiny raised spire is clearly visible in this view.
References for Trepospira sphaerulata
- Fossil works – Taxon Page
- Moore, R.C et al, 1960, Treatise on Invertebrate Paleontology, Part I, Mollusca 1, Page I201, I203
- Winchell, N.H., 1887, Geological and Natural History Survey of Minnesota: The Geology of Minnesota, V3, Pt2, Pg 1081.