NOTES ON AMERICAN SPECIES OF TRIACANTHAGYNA AND 

 GYNACANTHA (ODONATA) 



By E. B. Williamson 



During the past seventeen years many dragontiies from tropical America 

 have been added to my collection. From time to time, as material in certain 

 groups became of sufficient interest, reports on this material have been pub- 

 lished by others as well as myself. In this paper it is proposed to study the 

 specimens of the genera indicated in the title. During our held trips no effort 

 has been spared to make our collections of these striking insects as complete 

 as possible. 



These various trips may be briefly summarized as follows. I collected 

 in Guatemala and Honduras in 1905 and 1909. B. J. Rainey, my father, 

 L. A. Williamson and I collected in British and Dutch Guiana and in Trini- 

 dad in 1912. In 1916-1917, Jesse H. Williamson and I, as members of the 

 University of Michigan — Williamson Expedition to Colombia, collected in 

 that country. In 1920, H. B. Baker, W. H. Ditzler, Jesse H. Williamson and 

 I were the members of a collecting party for the Museum of Zoology, Uni- 

 versity of Michigan, in western Venezuela. The last three named devoted 

 most of their time to collecting dragonilies, and Mr. Baker, who was more 

 interested in other groups, brought in some specimens which are properly 

 credited to him in each case. Jesse H. Williamson collected in Peru in 1920, 

 and in Florida in 192 1. 



For all the assistance I have had. both from the members of the various 

 parties and from the University of Michigan, I wish to express my deepest 

 thanks. Mr. Rainey, Mr. Ditzler and ^Messrs L. A. and J. H. Williamson 

 not only joined these expeditions at their own expense but gave all their time 

 and strength in the field to collecting dragonflies, and their efforts and coop- 

 eration were the largest factor in the success and pleasure of these collecting 

 trips. 



The \'enezuelan collection especially was so rich in aeshnines of the two 

 genera Triacanthagyna and Gynacantha, embracing as it did no less than 

 twelve species, that it was felt the material on hand from all the trips could 

 be profitably reported on. This study was begun with the idea of making 

 such a report but early difficulties in the determination of certain specimens 

 compelled me to borrow material from other collections and to study 

 carefully all the species in the New World. 



Acknowledgements. Through Dr. Calvert I borrowed valuable material 

 from the Philadelphia Academy of Natural Sciences (abbreviated as .A. N. 

 S. in the text), and from him, with the kind consent of Mr. Henshaw, I also 

 obtained material belonging to the Museum of Comparative Zoology (ab- 

 breviated as AT. C. Z. in the text) which Dr. Calvert had borrowefl for study. 



