The pith-casts of Calamites are common Coal-measure fossils, sometimes of use in helping to fix the horizon of certain coals. They are, however, notoriously difficult taxonomically, and in several cases there is difference of opinion among authorities both as to the essential characters of a particular type of pith-cast, and also as to what is the most nearly correct name to apply to it. Immense space is still taken up by arguments as to what, exactly, some ancient and often manifestly rough drawing, supposed to represent a type, really depicts—with a view to maintaining a strict priority as regards nomenclature. If the original specimen is now lost, as is not infrequently the case, the guessing still continues. Some workers are not content to start their synonymies chronologically with the next oldest figure, the original of which still survives and the nature of which is agreed to on all hands.