NORTH AMKRICAN ODONATA. 



152a 



CATAI^OGUE OF THE ODONATA (DRAGONFLIES) OF 



THE VIC IJVITY OF I'HIEADEEPHIA, WITH 



AN INTRODUCTION TO THE STUDY 



OF THIS GROUP OF INSECTS. 



BY PHILIP P. CALVERT, 



Fellow in Biology, University of Pennsylvania. 



(Plates II and III). 



Such eminent authorities as the Baron de Selys-Longcharaps, Prof. 

 Uhler and Mr. McLachlan, have at different times expressed the 

 opinion that the number of species of Dragonflies is decreasing, at 

 least in well-settled districts. The causes for this decrease are prob- 

 ably to be found in the pollution of the waters in which the nymphs 

 live, and the filling up of ponds which formerly served as centres of 

 propagation. Such being the case— and it is also true of other groups 

 of animals— it seems advisable to bring together in permanent form 

 such records as exist of the dragonflies of Philadelphia and its neigh- 

 borhood, of their times of appearance, and of other biological facts 

 concerning them. While such a descriptive catalogue as the present 

 would be of greater value if it treated of a larger area, yet too large 

 a proportion of the species of the Eastern United States, for instance, 

 remain personally unknown to the writer to render such an extension 

 advisable. 



The data upon which the present Catalogue is based are— speci- 

 mens in the collection of the American Entomological Society, col- 

 lected chiefly by Mr. S. F. Aaron, and in that of the Wagner In- 

 stitute of Science by Mr. C. W. Johnson ; those gathered by Dr. 

 Henry Skinner and Messrs. C. W. Johnson, Philip Nell and Philip 

 Laurent, and generously placed by them at the writer's disposal; 

 while the principal source has been the writer's own observations 

 made in Delaware County, Pennsylvania, during the Summers of 

 1886-93. For the years 1888-92, a record was made each day for 

 each species observed, but other occupations prevented continuous 

 daily observations, so that future observers will probably add much 

 to the facts here given. 



TEANS. AM. ENT. SOC. XX. (19i) SEPTEMBER. 1893. 



