No. 4. — Illustrations of Odonata : Argia. By Hermann A. 

 Hagen. With a list and hibliographi/ of the species. By 

 Philip P. Calvert.^ 



The ijlustrations herewith presented require some words of explana- 

 tion. De Selys and Hagen intended pubUshing a Monograph of tlie 

 Agrioninfe, following a Synopsis of this subfamily, as they had for the 

 CalopteryginpQ and the Gomphina). The Synopsis a|)pcarcd in instal- 

 ments from 1860 to 1877. Hagen made drawings for the Monograph 

 which was never published, if indeed it ever was written. These, before 

 his death, were given to his friend and successor in the Museum of 

 Comparative Zoology, Mr. Samuel Henshaw. Some of these drawings 

 — those referring to the " grande genre Argia " — have recently been 

 lent to the present writer to be used in the study of material for the 

 Odonate part of the Biologia Centrali-Americana. So useful have they 

 thus proved, so desirable does it seem that others should have the 

 opportunity of using them, that they are here published. 



If justification were needed for this proceeding, it may be found in 

 these words of De Selys from the Synopsis of Argia, page 381 : 



" De grandes difficultes se presentent pour donner les diagnoses des quarante- 

 8ix especes americaines, dent plusieurs sont tres-voisines les uiies aux autres. 

 Les appendices anals des males et les lames du devant du thorax des femelles 

 fournissent, 11 est vrai, pour la phipart, des caractferes positifs ; mais ils eussent 

 rendu les diagnoses trfes-longues, et ces organes ne pouvent etre bien vus 

 qu'avec un certain grossissement, j'ai chercbe dans les diagnoses de ce Synop- 

 sis, k me passer de ces caracteres, (j^ui seront reserves pour une monographic 

 spdciale." 



As to the figures themselves, the original sheets on which they were 

 made bear the signature " H. Hagen del. 1864." As far as known, they 

 were executed without the aid of a camera lucida. It may be admitted 

 that they are not in all cases perfectly satisfactory, due partly to the 

 fact that the structures they depict were not sufficiently spread apart 

 to he clearly seen, as in Plate 2, Figs. 6 a, 14 a. It must also he borne 



^ The second-named author is responsible for the etitire text of this article. 



