International
Tables for
Crystallography
Volume A
Space-group symmetry
Edited by M. I. Aroyo

International Tables for Crystallography (2016). Vol. A, ch. 3.2, p. 735

Figure 3.2.1.5 

Th. Hahna and H. Klappera
[Figure 3.2.1.5]
Figure 3.2.1.5

The subgroups of the two-dimensional general point groups 16mm (4N-gonal system) and 18mm [[(4N + 2)]-gonal system, including the [(2N + 1)]-gonal groups]. Compare with Fig. 3.2.1.4[link] which applies only to one value of N.