LATE OSAGEAN AND MERAMECIAN ACTINOCRINITES (ECHINODERMATA, CRINOIDEA) FROM THE MISSISSIPPIAN STRATOTYPE REGION

Actinocrinites Miller from the Mississippian stratotype region of Illinois, Iowa, and Missouri are redescribed and redefined based upon study of the type material and morphometric analyses. Actinocrinites pernodosus, A. lowei, A. jugosus, A. gibsoni, and A. probolos n. sp. are recognized as valid species that occur in these strata. A combination of both metric and qualitative characters must be used to differentiate these species. Actinocrinites is known from the Montrose Chert Member of the Keokuk Limestone, the Keokuk Limestone, and the lower part of the Warsaw Formation, all late Osagean, in the stratotype region. In addition, Actinocrinites pernodosus and A. lowei are reported from the early Meramecian upper part of the Warsaw Formation, which is the first Meramecian occurrence of Actinocrinites in the stratotype region. Actinocrinites probolos n. sp. was ancestral to A. lowei, and the latter was probably ancestral to A. pernodosus. Nomenclatural and systematic acts include the following: 1) Actinocrinites lowei (Hall, 1858) is the senior synonym of Actinocrinus brontes Hall, 1860, Actinocrinites lobatus (Hall, 1860), and A. unicarinatus (Hall, 1860); 2) Actinocrinites jugosus (Hall, 1860) is the senior synonym of A. augustatus Miller and Gurley, 1894; and 3) the concept applied incorrectly to A. lobatus by Wachsmuth and Springer (1897) represents a distinct species, Actinocrinites probolos n. sp.