1913.] NATURAL SCIENCES OF PHIL.^DELPHIA. 249 



Steleopteron, also of the same age, its proximal edge is not as oblique 

 as in Tarsophlebia eximia and unbraced while its distal edge is more 

 oblique. So far as one may judge from Handhrsch's figures" of 

 Liassic Odonata the stigma was not oblique, or but moderately so, 

 and unbraced; the forms in which it is preserved, however, seem to 

 have but little relationship to the insects discussed in this paper. 

 The paleontological evidence, therefore, furnishes little encouragement 

 to use the stigma as a means of determining relationships.^^ It is 

 important to notice, however, from the accompanying Table I, 

 that the position of the stigma in the wing varies iDut little in different 

 genera and species, so that it constitutes a relatively fixed landmark. 

 9,11. The Points of Separation of M2 from Mi and of Rs from M1+2. — 

 Prof. Needham has noted®^ a minor line of development within the 

 Agrioninae, "in which nodus and quadrangle become more and more 

 approximate, and the veins M2, Rs, and Ms migrate separately along 

 vein Ml from their accustomed places toward the stigma." This 

 migration may be real or apparent. Retraction of the nodus with 

 no change in position of the separation point of M2 would result in a 

 greater interval between nodus and M2 and hence an apparent 

 movement of the latter toward the stigma, but no real movement 

 in respect to the wing as a whole. (Compare Table I, Thaumato- 

 neura, Rhipidolestes and Paraphlebia zoe cf .) 



Real migration is where the separation-point of M2 is transferred 

 distad considered in relation to the total wing-length, and may or 

 may not be accompanied by a change in the position of the nodus. 

 (Compare Table I, Perilestes and Dysagrion, and Perilestes, Argio- 

 lestes icteromelas 9 and Melanagrion.) These remarks will also 

 apply to characters 11 (the separation-point of Rs, including its 

 bridge where it exists, from M1+2), 14 (the separation-point of M3 

 from M1+2), 15a (the number of cross-veins proximal to the level of 

 the subnodus between Ms and M4) and 17a (the number of antenodal 

 cells between M 4 and Cui). In the preceding pp. 228-244, the state- 

 ments for these characters have been made with reference, not to the 

 wing-length, but to certain more or less varying landmarks, as the 

 arculus, nodus, or stigma; this course has been in conformity with 

 the established custom of descriptive writers. 



" L.c, Taf. XLII. 



^ Cf. Needham, Genealogic Study, pp. 710 at top and 730 at bottom. 



«3 L.c, p. 749. 



