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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 meeki is distinquished by its smooth convex, broad, nearly unornamented flanks, and smooth venter. Some Placenticeras meeki specimens occasionally possess small tubercles along the umbilical shoulder and some slight, broad, low ribbing. Placenticeras meeki can range up to nearly 32 inches in diameter.
Placenticeras: Placenta - means flat cake, ceras - means horn.
You see ammonites in books with these unusual alternating chamber colors, but seldom do you see one offered for sale. The top portion of the shell was crushed at some point. If you will notice at the top is a small Placenticeras specimen which has not been fully exposed. With a little additional work this could be made into a very nice piece.
This specimen also fluoresces. To see photos of this specimen under fluorescent lighting, go to the fluorescent section under South Dakota, specimen number FA-222F.
Placenticeras meeki
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Quantity in Basket:
None
Code: FAM-222
Price: $675.00
Shipping Weight: 3.79 pounds
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Time: Upper Cretaceous, Upper Campian, approximately 74-72 million years ago.
Location: Pierre Shale, South Dakota
Dimensions: 8-1/2 inches
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