During the Carboniferous and Permian period there were a group of Productid Brachiopods that grew to large sizes and had some odd body adaptations. Below are pictures of a genera called Reticulatia from the Permian aged Wolfcamp series of Kansas. These Brachiopods are identified best by the cross hatching pattern on their shells formed by crossing ribs and rays. You can see the pattern very clearly in the shell below.
This second specimen got to a ripe old age and has a very deep lip. Apparently the brachial valve grows generally flat but as they get older, instead of continuing to grow perpendicular, it parallels the pedicle valve and forms an exaggerated edge along the lip between the valves.