UK Heteromorph Ammonite Didymoceras
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Didymoceras stevensoni
Pierre Formation
Upper Cretaceous (Campanian)
Weston County, Wyoming
Here is an outstanding specimen of Didymoceras stevensoni from the Pierre Shale of Wyoming. This example is a museum quality specimen. It is expertly prepared and is a composite of two individuals. The specimen has considerable amount of original shell material preserved. This piece is prepared in its original matrix in which is embedded a nearly complete Solenoceras sp. There is also a loose Solenoceras sp. with the specimen that attaches to the first whorl. The conch is over 10 inches tall.

Didymoceras stevensoni is characterized in early growth by a loose elliptical u-shaped whorl starts out curved and enlarges to a loose helical whorl. These whorls grade into three broad helical whorls that are in contact with each other or nearly so. The conch terminates on a broad, shallow u-shaped body chamber. Ribs are broad and rectiradiate to rursiradiate. On the earlier whorls and limbs the rib-venter junction show tubercles on almost every rib. The venter is nearly flat and has two rows of tubercles. The genus name Didymoceras is derived from Latin for "paired horns".