A New Species of the Genus Boreophylloceras Alekseev et Repin, 1998 (Ammonoidea, Phylloceratida) from the Upper Ryazanian of the North of Eastern Siberia

A review of modern views on the position of Boreophylloceras Alekseev et Repin, 1998 in the phylloceratid system is carried out. Two opposing viewpoints on the assessment of the weight of taxonomic features of this genus, such as the very large size of the protoconch and ammonitella, the initial ventral-marginal position of the siphon, etc. are discussed. A new member of the genus B. subtile sp. nov. is described from the upper Ryazanian (Bojarkia mesezhnikowi zone) of the north of Eastern Siberia (Popigai River basin).