Barrande erected the genus Aristocystites, type A. bohemicus Barrande, in 1887. He listed other questionable species, including “A.? subcylindricus var. de bohemicus.” Aristocystites subcylindricus has not been accepted apart from Bather who in 1919 designated a type specimen and made it the type species of the new genus Hippocystis. No specimens available to Barrande or Bather preserved the oral area necessary to characterize Hippocystis or A. subcylindricus. Specimen 436969A, in the United States National Museum of Natural History is a more complete specimen of A. subcylindricus and preserves the oral area. This shows that A. subcylindricus is a valid species, but has two ambulacral facets, a character unique to the genus Aristocystites. Aristocystites subcylindricus has tumid plates with obvious sutures, a rounded thecal base, and a gonopore surrounded by three plates. Aristocystites bohemicus has smooth plates, an obvious attachment scar aborally and a gonopore within a single plate. Both species have occasional horseshoe-shaped diplopores.
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Vol. 93 • No. 4