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The Placenticeras genus is characterized by a tightly coiled (moderately involute umbilicus), lenticular (lens shaped), shell. The umbilicus (center) is well rounded and moderately deep. The flanks (sides) are broad, convex and ornamented, in some species, with ribs and tubercles along the umbilicus and midflank. The keel or venter (outside edge) is narrow and flat to slightly concave and protects the siphuncle. The siphuncle is the tube which connects the chambers allowing the animal to fill them with water or air to rise and lower in the water. Placenticeras has a very complex suture pattern with 10 to 14 divided, deep, narrow-necked saddles, lobes, and sinuses.
Placenticeras costatum is similar to its predecessor, Placenticeras intercalare, it has a thick whorl section, broad flanks, and prominent tubercles. It has two rows of tubercles. one row above the umbilical shoulder and the other approximately two-thirds of the distance from the umbilicus toward the ventral edge. The ribs are low, broad, and prorsiradiate, which originate on the umbilical tubercles and split into a pair of ribs that develop into the conical-shaped tubercles fartherest out on the flank. Placenticeras costatum also differs from its predecessor in both the suture pattern and its ventral edge. The three outermost suture lobes are more constricted in Placenticeras costatum. The clavi (small bumps) on the ventral edge number five between each pair of tubercles on the outer flank, as opposed to three in intetrcalare.
Placenticeras: Placenta - means flat cake, ceras - means horn.
This specimen has been sold! It was offered at $2,250.00.
Placenticeras costatum
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Quantity in Basket:
None
Code: FA-240
Price: $0.00
Shipping Weight: 6.27 pounds
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Time: Upper Cretaceous, Upper Campian, approximately 72 million years ago.
Location: Pierre Shale, South Dakota
Dimensions: 10 inches
This specimen has been sold!
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