124 Journal New York Entomological Society. [Voi. xl 



Angle of hu- 

 meral suture. 



Mi. Ma. Av. 



'Epiophlefhin-'E' 43 — — 



EpALLAGIN.t 51 67 62 



Vestai.in.^. 46 59 54 



-j tTHORIN.« 52 59 55 



IaGRIONID/E (Lestin.^ 59 66 62 



1 Agrionin^ 54 72 62 



Zygoptera 



■CALOPTERYGID.E- 



The above listed material was the best selection that could be made 

 from the material that happened to be at hand in the collection of the 

 senior author. Only papered specimens could be used readily. 

 Whole subfamilies are unrepresented, and the material used is insuffi- 

 cient to furnish a basis for true averages for any of the subfamilies. 

 Yet notwithstanding this, and with all due allowance for error in the 

 making of difficult measurements of angles, some general results are 

 sufficiently evidenced by the figures obtained. 



In the first place it is evident that the skewness of the thorax is 

 much greater in the Zygoptera than in the Anisoptera, the average of 

 the former being above the maximum of the latter. The minimum 

 for both angles measured is found in the ..r'Eschnimi?, and the maximum 

 in the Agrioninse. The widest range is shown by the Libellulinse, 

 and it is probable that this is due only in part to the selection of a 

 wider range of representatives of this subfamily. 



There was found less correlation between the two angles measured 

 than might have been expected. It will be observed throughout that the 

 maxima and minima rarely fall in the same places in the two columns. 

 The angle that measures the inclination of the humeral suture is with a 

 single exception greater than that measuring the tilt of the wing bases, 

 Epiophlcbia alone furnishing the reverse condition. 



There is little correlation between the size of the insect and the 

 inclination of the humeral suture : just how much, will be seen by 

 glancing down the first column, which in each subfamily is arranged 

 in accordance with the increasing angulation here. There appears to 

 be much more correlation between mere size and the tilt of the wing 

 bases: for it will be noticed in each group that the minimum falls 

 upon one of the largest and the maximum on one of the smallest 

 species. 



It must not be forgotten for a moment that these measurements take 

 no account' of possible parallelisms within the subfamilies, nor of di- 



