198 NEW YORK STATE MUSEUM 



confluent alofig the gill axis. This species has five setae on 

 each side of the mentum of the labium, and appears to be dis- 

 tinguished from the others hitherto described chiefly by the 

 possession of a spine on the lateral margin of abdominal seg- 

 ment 3. The lateral spines in this species occur on segments 

 3 to 9: in the other species on segments 4 and 5 to 9. 



The damsel flies of the following list were also collected 

 sporadically during the summer and all of them were appar- 

 ently common and widespread : Argia violacea.E rial- 

 lag ma exsulans, Enallagma hageni, Xehal- 

 lennia.irene, Ischnura verticalis. 



Contribution to the niorphology of the Odonata 



Three years ago I suggested to Mr O. S. Thompson, who 

 was then a student in my laboratory, that he investigate the 

 ihomologies of the male abdominal appendages of the Odon- 

 ata. There was then much confusion existing concerning the 

 terminal appendages, and no extensive comparisons of those 

 of the second segment had been attempted, the fragmentary 

 studies of Ratzeburg, Ingenitzky and Goddard being in the 

 nature of preliminary examination of a few forms. We. have 

 not known whether homologies are traceable through the 

 two suborders. These parts being used more and more as a 

 guide to relationships in the lesser groups, and as criteria of 

 species, it seemed important that their nature should be better 

 imderstood. Mr Thompson's work was done in 1904, but the 

 iinal preparation of his paper has been delayed by various 

 causes until the present time. Meanwhile, the terminal append- 

 ages have been carefully studied and fully reported upon by 

 Drs Heymons and Handlirsch. The results of Mr Thompson's 

 v^ork upon the other abdominal appendages, those of the sec- 

 ond segment, and adjacent thereto, are given at the end of this 

 article. 



