The structure of the proximal part of colonies of the Middle Ordovician Isograptinae and the species composition of the genera Oncograptus Hall and Cardiograptus Harris et Keble were discussed. Two new species Oncograptus hastatus sp. nov. and Cardiograptusaltaicus sp. nov. were monographically described when studying a collection of graptolites from the Middle Ordovician (Dapingian Stage) of Gorny Altai. These taxa are important for the zonal biostratigraphy of the Ordovician of southern Siberia and for interregional correlations.
