From the album: Brachiopods of Platteville/Decorah Twin Cities Minnesota
The major difference between S. billingsi and S. filitexta is the lack of enclosed muscle scars and S. billingsi tend to be smaller. #2 shows the difficulty for me - it shows a muscle scar - is it a broken enclosed one or is this normal for S. billingi? I don't know for sure. #3 S. billingi wasn't reported by authors as occurring into Platteville formation but I found shell hashes full of it into Mifflin Formation. I still have to look through a lot of individual platteville fossils in the future to see if other Strophomena species are represented - I have seen hints of possible S. septae. S. billingsi occurs in both Platteville and Decorah formation.