Trying To Id Silurian Rynchonellids

[Shamalama]

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.

[Malcolmt]

They look cool regardless presented like that....

[Quarryman Dave]

Like the way your presenting them

[Shamalama]

Thanks Malcolm and Dave. I tried a new way of comparing similarly sized specimens that I have multiples of. May do the same in the future for single genera that I have enough specimens of to present like this.

[erose]

What an excellent job you did. My experience in the Silurian is limited although it was where I began collecting back in Ohio. Considering the number of references you used I would say your IDs are probably pretty good. The one thing I found over the years was the value of building lists of known species for specific formations. Sometimes the readily available collector's references will only list the common species, while in fact there may be another two or three less well known to come across. Those can be harder to track down.

My catalog includes a field for "Identification Reference" where I note which book, paper or combination of such I used to make the final evaluation. That way as I get better material (both fossils and literature) I can go back and re-evaluate as needed.