Shell-like organism w/concentric circular center.

[GabeMan]

I found these two specimens in the Kansas City Group near the Fontana Shale. The first one is quite small, with a diameter of 9mm and a thickness of 2mm. The second one is larger at 12mm in diameter and 5mm in thickness. they also both have a ringed concave surface, as seen in the pictures, as well as a smooth, rounded outer shell. The first two and the last two pictures are of the smaller specimen the more close-up middle two pictures are of the larger one. The final picture is a side view of the larger one. Can someone please identify what these two fossils are for me.

[Fossildude19]

Looks like Orbiculoidea.

I have no idea on image 4.  Maybe a brachiopod, or gastropod, or pelecypod. 

Not complete enough to say for sure, in my opinion.

[Thomas.Dodson]

I agree that the first one looks like Orbiculoidea. I'd lean bivalve for image #4, that crosshatching pattern of growth lines crossing radiating striae is something I'd expect to see in bivalves, not brachiopods or gastropods. I can't be more specific though.

[DPS Ammonite]

Orbiculoidea are common in the Pennsylvanian rocks in the US. The shells are typically bluish grey or bluish black since they are phosphatic. I see remnants of the bluish grey shell circled in red in attached photo:

 

Edited 15 hours ago by DPS Ammonite

[Fossildude19]

1 hour ago, Thomas.Dodson said:

 I'd lean bivalve for image #4, that crosshatching pattern of growth lines crossing radiating striae is something I'd expect to see in bivalves, not brachiopods or gastropods. I can't be more specific though.

 

 

I would too, but then you have gastropods like Naticonema and Retispira leda.

 

Here is an image of a Retispira showing a similar texture.

 

 

I've also seen this type of texture on Naticonema gastropods, although I haven't an image to share. 

 

That said, I think bivalve is probably more likely. 

[DPS Ammonite]

Tim, the fossils are Pennsylvanian. The ones you suggested are older. 
 

Use the Dallas Paleo Society’s website to view many Pennsylvanian fossils. It sort of looks like a pecten like shell although shell scraps are hard to ID. Consider Euchondria.

 

https://www.dallaspaleo.org/Jacksboro-Study-Group

 

 

 

Edited 14 hours ago by DPS Ammonite

[Fossildude19]

50 minutes ago, DPS Ammonite said:

Tim, the fossils are Pennsylvanian. The ones you suggested are older.

 

 

Understood - and I already said I was leaning more towards bivalve.

You miss my point - I'm just pointing out the fact that the textures that are thought to be only bivalve related may not just be bivalve related. 

[DPS Ammonite]

2 hours ago, Fossildude19 said:

 

 

Understood - and I already said I was leaning more towards bivalve.

You miss my point - I'm just pointing out the fact that the textures that are thought to be only bivalve related may not just be bivalve related. 

I agree. A scrap like that could be part of a gastropod. We need to see more.