164 



proliiilily Injiiii'iKKii. yave ilie collectors several wild chases. Both Cele- 

 ihemis fasfinfa aiul J.ihtlhihi ><emif(iseiitt(t are almost certain to be taken 

 sooner or later. 



//. A New Diagnostic Character for the Species of the 



Genus AR(iiA. 



Clarence Hamilton Kennedy. 



The following- paper was undertaken 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. l)y which the 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 fhe ab- 

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

 of venation has not been attempted. The color pattern i.s notoriously 

 inadequate, and after careful comparison 1 find that the structure of the 

 prothorax and al>dominal appendages is equally so. 



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

 if eAer, used in classification. Avhich 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, just 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 

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

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

 Les appendices anals des males et les lames du devant da thorax des fem- 

 elles fournissent. il est vrai. pour la plupart, des caracteres positifs; mais 

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

 etre bien vus qu" avec un certain grossissement, j'ai cherclie dans les di- 

 agnoses de ce Syno]isis, a. me passer de ces caracteres, qui serout reserves 

 pour une monographie speciale."* 



■•' De Selys-Longchamps, Synopsis des Ag:rioninos, Bulletins de rAcadeniie roynle de 

 Belgique, 2me s?rie, tome XX, No. 8, p. (9). 



