Published online by Cambridge University Press: 14 July 2015
During preparation of a manuscript on new collections of Upper Cambrian trilobites from the Threadgill Creek section in central Texas (Longacre, 1970, text-fig. 6), a new trilobite species Ptychopleurites spinosa was discovered that can be used to recognize a revised base to the Saukia Zone (Trempealeauan Stage) in central Texas. This species is represented in central Texas by numerous, well-preserved cranidia and librigenae, but no pygidia have been recovered. Recently Ptychopleurites spinosa was also identified in a collection of trilobites of the partly correlative Illaenurus Zone (= lower part of Saukia Zone) from the type section of the Deadwood Formation in the Black Hills of South Dakota. This work is part of a paper that will describe the latest Franconian and Trempealeauan trilobites from the Deadwood Formation, using collections made by Dr. Christina Lochman-Balk. Ptychopleurites spinosa is represented in the Black Hills by incompletely preserved cranidia and well-preserved librigenae. Because it is not known which of these two papers will be published first, it was decided to establish Ptychopleurites spinosa as a new species with one of the better Texas cranidia as the holotype and the Black Hills material as part of the suite of paratypes.