Placas columnares de crinoides del Carbonífero de la región de Santiago Ixtaltepec, Municipio de Nochixtlán, Oaxaca; consideraciones estratigráficas y paleobiogeográficas

eleven crinoid columnal morphotypes of mississippian and pennsylvanian ages found in different stratigraphic levels of the santiago (informal unit) and ixtaltepec formations in outcrops in the santiago ixtaltepec region, municipality of nochixtlan, oaxaca, are reported and described. axilinucrinus angustus is proposed as a new morphogenus and new morphospecies. cyclocaudex insaturatus and floricyclus welleri have been found in middle mississippian (meramecian-chesterian?) strata from the upper member of the santiago formation. lomalegnum cf. l. hormidium, axilinucrinus angustus and one indeterminate genus are present in middle-late mississippian (meramecian-chesterian) strata of the ixtaltepec formation. pentagonomischus cf. p. plebeius and cyclocion distinctus occur in early-middle pennsylvanian (morrowan-desmoinesian) strata of the ixtaltepec formation. cylindrocauliscus fiski and cyclocaudex typicus are morphotypes with a broad distribution throughout the carboniferous section of nochixtlán. a strong similarity exists between all of the parataxa from oaxaca and those reported from lower mississippian-middle pennsylvanian faunas of the mid-continent region of the central eastern united states.