Middle Permian crinoids (Echinodermata, Crinoidea) from Cerros Los Monos, Caborca, Sonora, Mexico and paleogeographic considerations

crinoid columnals and pluricolumnals assigned to five species, pentaridica (col.) rothi moore and jeffords, cyclocaudex cf. c. (col.) jucundus moore and jeffords, cyclocaudex cf. c. (col.) costatus moore and jeffords, preptopremnum (col.) rugosum moore and jeffords, and heterostelechus (col.) texanus moore and jeffords, were studied from the permian beds of the monos formation which is exposed 50 kilometers west of caborca, sonora, in northwest mexico. heterostelechus (col.) texanus moore and jeffords is recorded for the first time in mexico. some crinoid samples preserve morphological features in the articular surface, allowing the species identification. the age of the fossiliferous strata was determined by the identification of fusulinids (parafusulina antimonioensis dunbar), ammonites (waagenoceras dieneri boese), and brachiopods (waagenoconcha montpelierensis (girty)) that are index fossils of wordian (middle permian) age.