What are these and how common are they?

[Zalgork]

I found a massive amount of these and was wondering what they are and how rare or common they are.  Found in a river bank in central Texas.  

 

 

 

 

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[calhounensis]

Reminds me a little of an Exogyra.  I don't believe that whatever it actually is would be that rare. Judging solely off the massive amount you have shown.

[Fruitbat]

Those look like the so-called 'Devil's Toenails', Gryphaea sp., a Cretaceous oyster.  They are not terribly uncommon in many Texas Cretaceous strata but those look like particularly nice ones.

 

-Joe

[JohnJ]

Ilymatogyra arietina oysters.  They are very common in the Main Street, Grayson and Del Rio formations. 

[fifbrindacier]

 

I vote for the Exogyra Ilymatogyra arietina.

Ilymatogyra arietina

[Herb]

I'm thinking Texigryphea sp. Nice finds but really common

[Darktooth]

A great addition to any collection!

[abyssunder]

 Ilymatogyra arietina (new name) =  Exogyra arietina (old name)

 

Wagih Ayoub-Hannaa & Franz Theodor Fürsich. Functional morphology and taphonomy of Cenomanian (Cretaceous) oysters from the eastern Sinai Peninsula, Egypt. Palaeobio Palaeoenv (2011) 91:197-214

 

A few Ilymatogyra arietina (Roemer, 1849) specimens are shown in Fig. 2 f-h.

[abyssunder]

Interesting is this specimen, which is nicely bored by a clionaid demosponge making those visible holes on the surface. So, you have a fossil oyster Ilymatogyra arietina with ichnofossil Entobia .