The genus Salopina Boucot (in Boucot et al., 1960) is now widely recognized in Silurian to Middle Devonian rocks (Walmsley et al., 1969); its Ludlovian type species is S. lunata J. de C. Sowerby (Walmsley, 1965). From the outset, a variety of morphs and named species have been gathered within the genus Salopina, although some significant differences have been evident. The most obvious difference is size, which is often ignored as a consequence only of ontogenetic variation. Size can also be a hallmark of habitat, or biofacies, or position in the benthic community chain.

Arceodomus Pojeta and Runnegar (1976) is a relatively rare genus of rostroconch. To date, four species have been reported in the literature: A. langenheimi (Wilson, 1970) from the Lower Permian McCloud Limestone in California; A. glabrata (Easton, 1962) from the Upper Mississippian Heath Formation of Montana and later, by Pojeta and Runnegar (1976), from the Upper Mississippian Diamond Peak Formation of Nevada; Arceodomus sp. from the Permian of the U.S.S.R. (Pojeta and Runnegar, 1976), based upon a specimen in the British Museum of Natural History; and A. aff. A. glabrata from the Pennsylvanian (Desmoinesian) Dickerson Shale Member of the Lazy Bend Formation in Texas (Pojeta and Runnegar, 1976).