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Central PA, Mifflintown-Bloomsburg (undividied) Block collected from roadsite float. Its pretty variable, with a flaky/fissile layers alternating with slightly more cohesive ones. Lots of broken brachiopod bits. For an experiment to I dropped an unremarkable flake the size of a large coin in some vinegar and let it soak for a day. The flake had a couple brachiopod bits and I wanted to see if they would fall free or dissolve in place. The brachiopds disappeared and I was left with this (see pics). Of course I got really excited and thought I had an early fish spine, but now I think I dissolved a crinoid stem and what we see is the matrix that filled in the soft bits. What do you think? Total length is 3/4"

Hey guys, I've been puzzling over some brachiopods that I've found at a site in PA that exposes the Mifflintown formation. This is a Silurian aged rock formation that is dated to about 428-420 mya (Sheinwoodian to Gorstian stages). It corresponds to the McKenzie formation in Maryland and West Virginia and a part of the Clinton Group in New York. The brachiopods are all Rhynchonellid types and look very similar. I've been able to split them into three somewhat distinct types based on the sulcus depth and size. Below is a picture of specimens of each type with the labels that I think go with them. I based my IDs on a variety of resources, many of which are very old and have older generic nomenclature. Among my sources were: "Index Fossils of North America" by Schimer and Schrock (1949) The "Silurian" volume from the Maryland Geological Survey (1923) "Silurian System of West Virginia" from the West Virginia Geological Survey (1941) "Fossil Collecting in Pennsylvania" from the Pennsylvania Geological Survey (1983) "Fossil Collecting in the Mid-Atlantic States" by Jasper Burns (1991) I'd appreciate any feedback or alternate ID suggestions.