Fossils of Australiaest. 2013
Leptagonia fossil2
FA-0373 · tap to enlarge

strophomenid brachiopod

Leptagonia sp.

Carboniferous346.7–330.9 Ma
Catalogue
FA-0373
Phylum
Brachiopoda
Class
Strophomenata
Order
Strophomenida
Family
Rafinesquinidae
Locality
Rouchel Brook district, New South Wales
Unit
Woolooma Formation
Age
Early Carboniferous (Viséan)
346.7–330.9 Ma
Reference
Wikipedia

A thin, broadly semicircular brachiopod with a straight hinge line and fine radiating ribs. The shell is concavo-convex — one valve domed, the other dished to match — so the animal lay almost flat on the sea floor.

That flat profile suited soft, muddy bottoms, spreading the shell's weight rather than letting it sink in.