Douvilleiceras mammilatum had a involute (tightly coiled) shell. It had simple and strong ribs that pass over a rounded venter (the outer edge of the ammonite). These ribs would have been divided into numerous even-sized tubercles, which would have had long spines.
This ammonite would have been a poor swimmer due to the presence of these ribs which would have brought about considerable resistance in the water. Because of this resistance, Douvilleiceras was probably a scavenger on the sea bed.
This specimen is a gorgeous polished agatized ammonite.
Kingdom: Animalia, Phylum: Mollusca, Class: Cephalopoda, Subclass: Ammonoidea, Order: Ammonitida, Family: Douvilleiceratidae, Genus: Douvilleiceras, Species: mammilatum.
Douvilleiceras mammilatum 
Quantity in Basket: None
Code: UAD-100
Price: $100.00
Shipping Weight: 0.52 pounds
Time: Late Early Cretaceous - approximately 135-100 million years ago.
Location: Unknown - Distribution is worldwide (location is most likely Madagascar)
Dimensions: 2-5/8" x 2" x 1-1/4"