164 



probably Jn/iiiriiaed. gave the collectors several wild chases. Both Cele- 

 iheniis fasciritu and LlheUuUi semiffisciata are almost certain to be taken 

 sooner or later. 



/'. A New DiaitXostic Character for the Species of the 



Genus Argia. 



Clarence Hamilton Kennedy. 



The following- paper was undertalien at the suggestion of Mr. E. B. 

 "Williamson, to whom the writer is also indebted for other suggestions 

 and for much of the material examined. 



The paper is the result of an attempt to find some character, if possi- 

 ble structural, by which tlie females of the five species of Argia found 

 in Indiana could be separated. 



The characters generally used in the classification of Odonata are the 

 venation of the wings, the shape of the prothorax, the shape of the ab- 

 dominal appendages, and the color pattern. A distinction upon the basis 

 of venation has not been attempted. The color pattern is notoriously 

 inadequate, and after careful comparison I find that the structure of the 

 prothorax and abdominal appendages is equally so. 



After a close study of the thorax a structure was discovered rarely, 

 if ever, used in classification, which in the case of the five Indiana species 

 is sufficiently different to separate the females readily. This is the pecu- 

 liar shield-shaped structure on the anterior end of the mesepisternum. 

 I can find no mention of this very peculiar structure except in Selys' 

 ''Synopsis des Agrionines."' Here, .iust as I was finishing this paper, I 

 found the following, in which Selys recognizes the diagnostic value of 

 this character in the case of the females of the genus Argia: "De grandes 

 difficultes se presentent pour donner les diagnoses des quarante-six especes 

 (Argia) Americaines. dont plusieurs sont tresvoisines les unes des autres. 

 Les appendif-os anals des males et les lames (In decant an thorax des fem- 

 elles fournissent. il est vi-ai, pour la plupart, des caracteres positifs; mais 

 ils eussent rendu les diagnoses tres-longues, et ces organes ne pouvant 

 etre bicn vns (]u' avec un certain grossissement, j'ai cherche dans les di- 

 agnoses de ce Syno])sis, a me passer de ces caracteres, qui seront reserves 

 pour une monographic speciale.'"* 



'•■ De Selys-Longchamps, Synopsis des Agrionines, Bulletins de I'Aeademie royale de 

 Belgi<iue, 2me s'rie, tome XX,Xo. 8, p. (9). 



