1	Shell surface with radial ridges covering the entire shell disc	I.subclathrata (Martens, 1899)*
–	Shell surface without radial ridges on the shell disc	2
2	Shell surface mostly smooth, while regular ridges cross the growth lines and form a clear rectangular pattern in the posterior-dorsal area, and curved, lamella-like ridges closely spaced along growth lines in the anterior-dorsal area	I.rectangularis (Tapparone-Canefri, 1889), comb. nov.**
–	Shell surface smooth	I.andersoniana (Nevill, 1877)***