Fort Worth creek fossil ID

[Creek - Don]

I found all of these today at Fort Worth creek.   I Identified most, like ammonite, nautiloid, gryphaea, bivalves, echinoids, but on the picture 2, what is that?  Is that a oyster or a clam?   Fourth picture is a mass gryphaea bed. 

[Creek - Don]

[grandpa]

12 minutes ago, Creek - Don said:

, but on the picture 2, what is that?  Is that a oyster or a clam? 

Rastellum (Arctostrea) carinatum (Lamarck, 1819)

[Creek - Don]

Great! Thanks grandpa.