was described by Brown in 1912 as a new genus and species of glyptodont, Brachyostracon cylindricum. Brown also recombined Glyptodon mexicanum into Brachyostracon mexicanum. Brachyostracon is now seen synonymous with Glyptotherium on the genus level, but G. cylindricum is a valid species. In 1923, Oliver Perry Hay named a new species of Glyptodon, G. rivipacis, based on the fossils described by Leidy from DeSoto County, Florida. This species is now seen as a nomen nudum and synonymous with Glyptotherium cylindricum. Hay also described well preserved fossils, including skull elements and teeth, that were collected from Rancholabrean strata in Wolf City and Sinton, Texas that were referred to Cope's Glyptodon peltaliferus. These fossils have since been referred to G. cylindricum. A third genus of North American glyptodont, Boreostracon floridanum, was established by George Gaylord Simpson in 1929 based on several isolated specimens unearthed by the AMNH from Rancholabrean age localities in Florida, the holotype specimen being the rear portion of a carapace recovered from Seminole Field locality in Pinellas County, Florida. Simpson referred all of the fossils previously described from Florida to B. floridanum and believed that all of the glyptodont fossils unearthed from North America were not of Glyptodon. However, Simpson didn't designate a new genus or species for Glyptodon peltaliferus, but he still believed that they were from a separate form of glyptodont. Boreostracon floridanum has been synonymized with Glyptotherium cylindricum. Research into North American glyptodonts diminished after the research of Gidley, Hay, Simpson, and others, but some paleontologists still incorrectly referred fossils from the continent to Glyptodon. Throughout the 1920s and 1930s, many Early Pleistocene age fossils were collected from a locality in Frederick, Oklahoma, including several fragmentary fossils of glyptodonts, horses, gomphotheres, and camels. These glyptodont fossils were described as a new genus and species, Xenoglyptodon fredericensis, in 1953 on the basis of a partial lower jaw and several teeth. The species has been synonymized with Glyptotherium texanum. After all of these genera were named, a great reassessment wasn't conducted until 1981, David Gillette and Clayton Ray published a monograph on North American glyptodonts. In their monograph, they recombined all previously named genera and species into Glyptotherium, synonymized some species, and also researched the genus' ecology, anatomy, and distribution. However, G. arizonae, G. floridanum, and G. mexicanum were kept as valid species, all of which were synonymized with G. texanum and G. cylindricum after the discovery of