Asteroceras obtusium
 
Asteroceras obtusium, Sowerby 1815
Charmouth, Dorset Coast.
 
Family ARIETITIDAE Hyatt, 1874 Subfamily ASTEROCERATINAE Spath, 1946
 
A zone ammonite of the Upper Sinemurian Substage.
 
Ribs strong and smooth, curved forward. Whorls high, enlarging rapidly, sides converging above the middle, keel large, prominent, flanked by 2 deep sulci which are lost on outer whorl. Size 15cm across.
 
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