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Zygospira sp. Apparently there are a mystery with this genus when it comes to Twin Cities. I first noticed it only from Middle Platteville Formation - 100% nonexistent from upper Platteville Formation. Much more finer costae compare to Rostricellula minnesotensis and generally smaller. Belongs in Spiriferid family despite it strong resemble to Rhyconellid family. Then after a very long absent either the same species or a very similar species popped up again in upper Decorah formation and became very abundant. I suspects the reason for this seemly weird pattern is they may be much more specialized into the type of sediments that laid on the ocean floor. The middle platteville had layers of high carbonate shale mixed in, which does not exists in upper and lower Platteville formation. Then upper Decorah formation had a harder type of shale - middle and lower Decorah formation have shale that breaks into pieces very easily. Plus from my experiences with modern Florida gastropods there are two endemic species of gastropods that had very narrow ranges. One I don't have specimens of is Sanbriel Island turret snail which is endemic to southwest mainland Florida. Not found anywhere else. The other snail species, Shiny Atlantic auger, Hastula hastata is only found generally around Jupiter Island on Atlantic side. At first it may seem like the two snail species have nothing in common but I find it interesting that they occurs in a small zone in between the carbonate sediments of far southern Florida to the keys and the sandy rubble to the north.