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Tiesta, February 7, 2015 in Minnesota
Next is a unidentied genus from mifflin which I feel are most likely belong in Trochoidea. It have no ridges, just smooth round coils. The weird thing is when I accidently broke one cast mold I found out the inside coils are well preserved and have mother of pearl shell. That's what confirm me since it have Trochoidea like spires and Trochoidea is also well known for its mother of pearl which can be visible when you shave away the outer layer of shell. After all since winged oysters already have fossils in Ohio in upper Ordovician so why not top shells. Scallops actually start a few epochs later so I figure most modern day shells actually got started during those ages.
Trochonema umbilicata is different into its coils are more squashed, kinda similar to Fusispira nobilis. Most of what I finds are in decorah usually missing the tops of their spires. It's ridge are kinda 2/3 of the way down the individual coils and are smooth.
Clathrospira subconcinna differs from the others into having its smooth ridge down at the bottom of each coils, giving it a distinct cone shape. I find it into platteville magnolia, decorah and galena making this one tough genus to survive numerous volcano eruptions nearby that occurs during late Ordovician. That's what interesting since you start with sandstone in which very uniform grains high in silica and purity then sudden that got cut off and then small amount of shale began, then all of sudden dolomite appear and continue for a while then again all of a sudden the magnesium ions used to make dolomite disappear, so shale become dominant with varying amount of shaly limestone mixed in. Three classic sedimentary rocks not that far apart which is pretty extreme along with big changes in sea levels similar to ice ages.
Last of the identified species is Lophospira spironema. It's different from similar genus into having a single pronounced ridge along the middle of the spire that's continuous. Platteville magnolia, decorah and galena.
After looking at whatever left of platteville I think I need to break in groups one have two pronounced ridges instead of one.
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