In defining the different species of the genus encrinurus (Emmrich) use has frequently been made of the disposition of nodes on the rings of the mid-lobe of the tail-shield. It is largely by this diagnostic that Foerste, for example, distinguishes E. thresheri from E. ornatus. Hall and Whitfield and the latter authors again, use the same criterion in separating E. ornatus from the European species figured in Murchison's Siluria.
Proceedings of the Iowa Academy of Sciences
©1895 Iowa Academy of Science, Inc.
Norton, William Harmon
"Variation in the Position of the Nodes on the Axial Segments of Pygidium of a Species of Encrinurus,"
Proceedings of the Iowa Academy of Science, 3(1), 79-81.
Available at: https://scholarworks.uni.edu/pias/vol3/iss1/23