While preparing the part of the Treatise on Invertebrate Paleontology dealing with Greenfieldia, Alvarez had problems with the absence of information regarding its jugum. GRABAU (1910, in Grabau and Sherzer) described the smooth, subequally biconvex, small shell Greenfieldia whitfieldi, the type species of his Greenfieldia, from the Late Silurian Greenfield Dolomite of northern Ohio. Grabau (1910, p. 149) remarked that the brachidium was unknown, with only the presence of laterally directed spiralia (Grabau, Pl. XXX, fig. 9) being indicated but not discussed in the text. Grabau (1910) considered a questionable assignment of Greenfieldia to the meristelloid Hindella. Boucot et al. (1965, p. H662), Berry and Boucot (1970, p. 155) and Berdan (1972, p. 16) all illustrated the difficulty in discriminating between the Late Silurian Protathyris, whose jugum is known and athyroid in type, and Greenfieldia with its unknown jugum. Jones (1978, p. 10) further emphasized the difficulty in discriminating between Protathyris and Greenfieldia owing to ignorance of the latter's jugum. Modzalevskaya (1979, fig. 7) described a jugum from a form assigned to Greenfieldia. The complex form of the jugum she illustrated, featuring a number of recurving branches, is entirely unlike that of Greenfieldia although relatively similar to that of Protathyris.