Here are another couple of Ammonites from the Carlile shale member of the Mancos Shale (Turonian stage of the Cretaceous) of Sandoval County, New Mexico. They are specimens of Spathites puercoensis. This ammonite is small but somewhat robust with some obvious ribs near the keel. Each whorl overlaps the previous by about 95%. As these are steinkerns and no original shell is left, the suture pattern is easily visible and consists of a number of alternating "U" shapes, of differing depth, accented with some smaller zigzags.
A cross section view of the last suture chamber
Right side (note the rock plug in the center which indicates there were likely more whorls that eroded away before the fossil was found)
Cross section view of the last suture.
A closer view of the suture pattern.
The publication "Contributions to Late Cretaceous Paleontology and Stratigraphy of New Mexico Part II". Bulletin 114. New Mexico Bureau of Mines and Mineral Resources. contains a paper by W. A. Cobban titled "The Late Cretaceous ammonite Spathites Kummel and Decker
in New Mexico and Trans-Pecos Texas" from which this illustration of the suture patterns of S. puercoensis comes.
Thanks to Mike (PFooley on the Fossil Forum) for this fossil that he offered up as part of an auction to help defray some of the operating costs of the Fossil Forum website.