Fossil specimen of a stem base of the horsetail (Equisetophytes) *Calamites suckowi* from the Pennsylvanian of Pennsylvania (PRI 50479). Note the characteristic nodes (horizontal lines) and internodal ribs (vertical lines). Specimen is on display at the [Museum of the Earth](http://www.priweb.org), Ithaca, New York. Length of fossil is approximately 21.5 cm. Model by Emily Hauf.