Sunday, March 13, 2011

Ilymatogyra arietina

Another oyster found in the Cretaceous sediments of Texas is this curled specimen. Below is what I believe is a Ilymatogyra arietina based on the book "A Field Guide to Fossils of Texas" by Charles Finsley, plate 58, photo 192.

This fossil comes from the Lower Cretaceous aged Grayson Fm., Denton County, Texas.

As a comparison, here are the three Texas oysters that I've detailed in the last few posts side by side. From left to right: Texigryphaea navia, Texigryphaea marcoui, Ilymatogyra arietina


  1. Hi - I save yesterday's Waldron Shale FM post. I'm thinking that the unknown fossil is Dalmanella elegantula. It's hard to tell from pictures, but it looks right.

    Best regards - Jack Kesling /Drexel Hill, PA

  2. Hi Jack, Thanks for the comment. I'm not sure about the Dalmanella ID as most specimens that I've seen are from the Ordovician and are flatter in profile while the shell I posted is from the Silurian. Also Dalmanella have a well defined, triangular interarea and a wider hinge line, unlike the specimen I posted.