1913.] NATURAL SCIENCES OF PHILADELPHIA. 251 



The paleontological evidence with reference to the separation- 

 points of iVIi, Rs and AI3 is that the Liassic fossils (with the exception 

 of Protomyrmekon) had M2 separating at the subnodus, and Rs 

 (including its bridge) and Ms proximad to the nodus;" none of these 

 fossils which have the nodal region preserved are considered by 

 Handlirsch to be ancestral to Zygoptera, however. For many of 

 the Jurassic remains^^ the same statement as to the positions of these 

 separation-points holds true, including Tarsophlehia eximia and 

 EuphcEopsis multinervis; Steleopteron had Rs and Ms arising well 

 proximad to the nodus, M2 only a short distance distad to the nodus; 

 Palceophlebia synlestoides, which Brauer, Redtenbacher and Gangl- 

 bauer assigned to the legion Podagrion of Selys^^ but which Hand- 

 lirsch regards as an Anisozygopter of doubtful position,'^^ is imperfectly 

 preserved, but seems to have had the origins of both Rs and M2 

 distinctly distal to the nodus, while that of Ms was probabh' proximal 

 to the nodus. Paleophlebia came from the Dogger, or lower Jurassic, 

 of Siberia, and is therefore older than the other Jurassic fossils just 

 referred to, all of which are Malm or Upper Jura. The paleontological 

 evidence is consequently not altogether satisfactory and at least 

 admits of the possibility of the separation-points of these three veins 

 having fluctuated proximad or distad from time to time. Prof. 

 Needham's statement as to their migration, quoted above, has not 

 that evidence from other sources than comparative morphology 

 which is necessary to enable us to use these characters with perfect 

 confidence. 



13. The position of the arculus has been relatively stable, so that there 

 is little reason for attaching any special phylogenetic value to it. 



14. The Point of Separation of il/s frotn M1+2. — (See the discussion 

 above under Nos. 9, 11.) 



15a. The Number of Cross-veins, Proximal to the Level of the Sub- 

 nodus, between Ms and Mi. — This character is closely dependent on 

 No. 14, for the more proximal is the separation-point of Ms from Mi+2, 

 the greater is the area available for these cross-veins. In the genera 

 here compared the greatest number of cross-veins, two, is found in 

 Phenacolestes, Lithagrion, and Melanagrion, all of which have a more 

 proximal origin of Ms. The reverse case is not necessarily true, as 

 Philogenia, Allopodagrion, and Dysagrion, with an equally proximal 



73 Handlirsch, Foss. Ins., Taf. XLII. 



^1 L.c, Taf. XLVII. 



75 Mem. Acad. Imp. Sci. St. Petersb., (7), XXXVI, p. 6, 1889. 



'« Foss. Ins., p. 584. 



