Selection of extant stonefly forewings for comparison with fossil material. A-D, Acroneuria abnormis Newman, 1838; A, Specimen IWC OB 799 (♀), left forewing; B-C, Specimen IWC OB 800 (♀); B, Left forewing; C, Right forewing; D, Specimen IWC OB 810 (♂), right forewing; E-H, Acroneuria carolinensis Banks, 1905 (large arrows indicate various conditions of the connection between MP and CuA); E, Specimen IWC OB 833 (♀), left forewing; F-G, Specimen IWC OB 834 (♀); B, Left forewing; C, Right forewing; H, Specimen IWC OB 838 (♂), left forewing; I-L, Pteronarcys californica Newport, 1851 (large arrows indicate various conditions of the connection between RP and MA); I-J, Specimen IWC OB 816 (♀); I, Left forewing; J, Right forewing; K-L, Specimen IWC OB 824 (♂); K, Left forewing; L, Right forewing; M-P, Pteronarcys princeps Banks, 1907; M-N, Specimen IWC OB 828; M, Left forewing; N, Right forewing; O-P, Specimen IWC OB 830 (♂); O, Left forewing; P, Right forewing. RP and MP branches indicated by blue and red dots, respectively; r-m fold indicated by a dashed line.