Spinaptychus in Texanites(?) sp.
Austin Chalk. (Upper Cretaceous Campanian)
Tarrant County, Texas
Sold Rex Williams New Zealand

Here is a real rarity! This ammonite (Texanites?) from the Austin Chalk of Texas has a very well preserved Spinaptychus in the body chamber. Like other aptychi, Spinaptychus occurs in bilaterally paired valves, which are thought to have served as opercula for the shell of ammonoids. Each valve is slightly arched. The concave surface, which is marked only by growth lines is interpreted to be the inner surface of the operculum attached to the flesh of the mantle. This specimen is comparable with a published description of Spinaptychus in Texanites from the Upper Cretaceous of Zululand (see Kennedy WJ Klinger HC, 1972, Paleontology V15, p 394-399). Very few examples of Spinaptychus have been found still in place in ammonite living chambers.