The diversity of pelecypods that are found within the Devonian aged (Givetian stage) Moscow formation is pretty amazing. At a time when brachiopods were still somewhat dominant, pelecypods had become a strong part of the ecosystem in their own way. That is why I love it when I find another species that I've never seen before. Pholadella radiata is the muse of this post and is a nicely decorated shell that reminds me of the extant Arcidae family of shells. The specimens I found are all small, about an inch (2.5 cm) or so in length. It has a sweeping form on one side which contasts to the otherwise rectangular shape. Sharp radiating striae (lines on the surface of the shell that extend out from a common point) cross, generally, delicate concentric growth lines. It is this somewhat geometric decoration that makes it easy to ID in the field. I don't have any fully inflated specimens with both valves but you can see what they should look like in the pictures below.
This piece has numerous individuals all clustered together. It was part of a larger plate that broke apart as I was extracting it.
Here is a solo valve (the left valve I believe)
And a couple of right valves from different individuals.
All the pictured specimens come from the Deep Springs Rd. quarry near Earlville, NY which exposes the Windom shale member of the Moscow formation.