I'm trying to identify this fossil. It was collected in Pennsylvania (exact location unknown), about 50 years ago. The length is over 2 feet and the trunk is a little more than 3 inches wide. It is clearly some sort of scale tree, but the leaf scars are not diamond shaped as in Lepidodendron, or vertical aligned (and no ribs) as in Sigillaria. They may be in a spiral patern. The trunk markings look similar to roots, but there are clearly attached grass-like leaves along both sides (which means that the leaf scars are not worn, as they would be lower down a trunk). Any ideas?