I've had this fossil for 20 years and I have not been able to identify these structures. Does anyone recognize them? The matrix is a hard, grey green shale(?) and the structures are dark brown. I believe it's age is Devonian. Other fossils found at the same spot are brachiopods and horn coral. I have looked all over to find something similar with no luck. Sorry for the poor picture quality. I only have the camera on my phone which is pretty old. Thank you in advance for any help or suggestions.