Vanuxemia Or Cyrtodonta

[Tethys]

This is another piece of algal biostrome filled with fossils from the Prairie du Chein at Stillwater, Minnesota. This shell is much better preserved than most pelecypods in this formation because it is on the sole of the bed within the aperture of a large coiled mollusk. (I can't tell Bucania from Protowarthia but both are possibilities) Bivalves are usually found as separated adjacent halves, completely covered in vuggy crystals. This valve is only slightly overgrown by the algae so I can still see shell material. There are also a tentaculites and two different large orthid brachiopods encrusting the coiled mollusk; in addition to the encrusting algae. The brachiopods are molds and casts with occasional preserved shell. One is flat bottomed, winged form like Vinlandostrophia, and the other is a broad rounded variety. I took many photos, some are clearer than others. The first photo is for perspective, showing the shell in question within the aperture. There is thick shell visible just below my thumb, and on the far side of the bivalve. Rotated 180 degrees.

[Tethys]

More close ups. There is a brachipod cast partially visible on the far right side. Edited to add measurements. It is 31 mm from beak tip to end, 20 mm in width at the widest point, and 14 mm across the hinge. I see three teeth within the shell and an articulating socket at each side but my reference doesn't have any illustrations of the interior anatomy.

Edited March 30, 2015 by Tethys

[Tethys]

Just to share, a piece of upper Cambrian Franconia formation green siltstone with both valves of a Pterinea and one of maybe Modiolopsis. These are quite small, the long single valve is 21 mm, and the winged valve is 17 mm x 12 mm.

Edited March 30, 2015 by Tethys