104 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



in mind by those using them that the apparent shape of the appendages 

 of the males depends very largely on the particular angle at which they 

 are viewed, and that the appendages themselves are capable of a consid- 

 erable degree of rotation. The seeming differences between the two 

 figures of Argia tibialis, Plate 2, Figs. 7, 7 a and 8, 8 a, are readily ex- 

 plained in this way, as any one who will compare them with a male of 

 this species may convince himself. Yet no one who has attempted the 

 study of this difficult genus will question the value of the aid which 

 these figures offer in elucidating the species all too briefly described in 

 the Synopsis of 1865, remembering also that their originals are scattered 

 through several museums of Europe and America. The arrangement of 

 these illustrations on the plates has been chi-efly guided by two ideas : 

 to place similar shapes near together for ease of comparison, and to 

 associate species which from personal knowledge are believed to be 

 related. 



It has been thought desirable to accompany these figures with a list 

 and bibliography of all the known species of this group. The list has 

 been arranged alphabetically for convenience' sake, since the writer has 

 too little acquaintance with the South American species to attempt to 

 place them in their proper relationships, while, on the other hand, for 

 reasons given elsewhere, he cannot subscribe to the classification em- 

 ployed in the Synopsis of 18G5. It is hoped that the bibliography 

 embraces references to all descriptions and figures, but mere locality 

 lists are not necessarily included. The distribution of each species is 

 given in a general way ; details will be found in the authors quoted. 

 Two works which togetlier contain descriptions of all the known species 

 are cited in abbreviations. These are : De Selys-Longchamps, Synopsis 

 des Agrionines, 5me legion : Agrion, Le grand genre Argia (Bulletin Acad. 

 Eoy. Belg. — 2 — XX., pp. 375-417, 1865), which is quoted simply as 

 " Argia ; " since the paging of the separate copy is different, the page 

 number of this latter is also given, but in parentheses ( ). While this 

 Synopsis is published as under the authorship of De Selys, many of the 

 descriptions were written l)y Hagen, and in sucli cases due credit is 

 given to the latter. The other work is Calvert : Odonata in Biologia 

 Centrali-Americana, Neuroptera, pp. 17 et seq., London, 1901-02, here 

 shortened to "B. C. A." 



As far as possible, the present location of the types of each species is 

 given from personal knowledge and from the literature. 



The two closely related genera Uyponeura and Onychargia have been 

 included. 



