Genus Caneycycloceras Niko & Mapes, 2011 Type species Caneycycloceras girtyi Niko & Mapes, 2011. Diagnosis Genus of the family Brachycycloceratidae with an exogastric, rapidly expanding, weakly cyrtoconic juvenile conch and a strongly inflated adult conch. Juvenile conch with circular conch profile. Juvenile conch strongly annulate, shell surface with fine growth lines; adult conch weakly non-annulate. Siphuncle nearly central, septal necks questionably suborthochoanitic. Species included Arkansas (Niko & Mapes 2011): Caneycycloceras girtyi Niko & Mapes, 2011. Rhenish Mountains (this paper): Caneycycloceras rotersorum sp. nov.; Caneycycloceras fuerstenbergorum sp. nov. Remarks Niko & Mapes (2011: 293) gave a diagnosis to separate their new genus from Brachycycloceras: “Shell characterized by more rapid expansion (28° to 30° in angle) and slightly stronger endogastric curvature (radius of curvature = ca 8 cm) of immature shell than Brachycycloceras that is assigned to the same family; siphuncle supracentral with a nearly central position; mature shell indicates slightly contracting tendency to aperture; periodic transverse constrictions are developed in adoral part of mature shell.” They also stated that the position of the siphuncle is the most distinctive feature: “In the new genus, the siphuncle is located near the conch axis with position ratios (distance of central axis of septal foramen from internal shell wall of venter to corresponding dorsoventral internal shell diameter) approximately 0.53, whereas the siphuncle position of Brachycycloceras is near midway between the conch axis and the dorsal margin, whose ratios of the siphuncular position are approximately 0.7–0.8.” Besides this, the expansion angle is larger in Caneycycloceras (28°–30°) than in Brachycycloceras (13°–15°). Two additional new species are assigned here to Caneycycloceras. Unfortunately, both are known only from their juvenile conchs, so it remains uncertain whether they also developed the bulbous adult stage characteristic of the type species. However, the morphology of the annulate portion of the conch supports their placement within the genus Caneycycloceras.

Published as part of Korn, Dieter & Aubrechtová, Martina, 2026, New annulate Carboniferous orthoconic and cyrtoconic cephalopods of the family Brachycycloceratidae Furnish, Glenister & Hartman, 1962, pp. 1-39 in European Journal of Taxonomy 1048 on pages 23-24, DOI: 10.5852/ejt.2026.1048.3231, http://zenodo.org/record/19335382