Macrocystella? durandin. sp. (Echinodermata, Rhombifera) and new data on the genus Macrocystella in the Cambrian-Ordovician boundary beds of northern Argentina

The new species Macrocystella? durandi n. sp. is characterized for the Tremadoc of Northern A rgentina, and six new localities bearing the genus Macrocystella CALLAWAY within the Argentine Cordillera Oriental are introduced. The fossiliferous material comes from shale and sandstone levels of the Casa Colorada, Alfarcito, Rupasca and Saladillo ormations (Santa Victoria Group), that crop out in different localities of the Quebrada de Humahuaca (Jujuy Province), and the Angosto de la Quesera (Salta Province). The biostratigraphic framework of the fossils is also given, showing the oldest record of Macrocystella CALLAWAY in the Upper Cambrian of the Casa Colorada formation at the locality of Pintayoc, north of Humahuaca town (Jujuy Province). A discussion on the taxonomy of the genus is given, analysing the information published until now within the  rgntine - Bolivian cambro - ordovician basin. Macrocystella? durandi n. sp.differs from the rest of the species of Macrocystella by its delicate ornamentation on the thecal plates, with fine and numerous folds, as well as by the possible pectinirrombs developed on some fields between the main (axial and radial) folds.