Autapomorphies of Baetisca/f3=g2.

(1) In imago abdominal tergum VI [enlarged – see Posteritorna (5)] has mid-dorsal elevation with transverse crest, similar to that of larva. 

(2) In female imago posterior margin of abdominal sternum IX produces a pair of projections with a median cleft between them (Pescador & Peters 1974: Fig.25C). Non-unique character, the same in many other mayflies (but not in Balticobaetisca). 

Characters of Baetisca/f3=g2 of unclear phylogenetic status (unknown for Balticobaetisca).

(3) 2^nd (penultimate) segment of labial palp has apical projection on inner side (Eaton 1883-1888: Pl.52:9; Pescador & Peters 1974: Fig.15E). Non-unique apomorphy (see Index of characters [1.1.58]); as mouth apparatus of Prosopistoma/f1=g2 is strongly modified, it is not clear if this is an apomorphy of Baetisca/f2=g1 or Posteritorna in general.

(4) Larval notal shield [see Posteritorna (3)] has a pair of lateral projections, which in different species have shape from small blunt protuberances to large pointed spines (Pescador & Berner 1981: Fig.10-14); they can increase from instar to instar (Pescador & Peters 1974: Fig.10,11,14).

(5) On fore legs of male imago and subimago both claws are blunt (Pescador & Peters 1974: Fig.24C). Non-unique apomorphy (see Index of characters [2.2.77]); possibly this is an apomorphy of Posteritorna in general, because Prosopistoma/f1=g2 has more simplified claws [see Prosopistoma/f1=g2 (4) above].