The Sphenodiscus genus is described as having a smooth planispiral, lenticular-shaped shell with a closed or involute umbilicus (center). The flanks (sides) are wide and very broadly convex, and the venter (outside edge) is narrow and acute. The suture pattern of this ammonite is fairly simple, with about eleven or twelve rather short, deeply divided lobes.
Sphenodiscus: Spheno means - a wedge, discus means - a disk.
Sphenodiscus sp. 
Quantity in Basket: None
Code: FA-250
Price: $225.00
Shipping Weight: 1.37 pounds
Time: Upper Cretaceous, Lower Maastrichtian, approximately 69 million years ago.
Location: Pierre Shale, South Dakota
Dimensions: 5-5/8 inches