670 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxkvi. 



3. The genus Gomphus is chiefly the guardian of the river. The 

 species may be seen at all times of day patrolling the river's surface 

 with tireless vigilance or squatting upon the shore and watching their 

 surroundings intently, and woe betide the luckless insect that comes 

 within their reach. All of the species observed are remarkably alike 

 in their habits so that it is practically impossible to distinguish them 

 until after they are caught. This genus also was found universally 

 distributed and not colonized. 



4. The other dragonflies and the damsels, on the contrary, Avere 

 found in colonies, each made up of a few closely related species that 

 harmonize well with one another and restricted in its area with 

 fairly well-defined borders. A few of these colonies are worthy of 

 special mention. 



A. The first was at Beaver Lake in St. Paul and was made up of 

 Lihellula exiista Say and L. quadnmaculata Linnseus for the dragon- 

 flies, and Enallagma Jiageni Walsh for the damsels. The lake is 

 small and surrounded by a scattering growth of underbrush and 

 rank grass. There were hundreds of the dragonflies among the 

 bushes and shrubs, while the tufts of grass were so loaded with 

 Enallagma that a single sweep of the net secured over two hundred. 

 While other species were found, as given in the list, it was only after 

 long and careful search and in such small numbers as to count for 

 nothing beside the myriads of the three species mentioned. 



B. Another colony was found on the bank of the St. Croix River, 

 opposite Stillwater, Minnesota. Here had been formerly a large saw- 

 mill, and the river bank for a long distance was packed with sawdust, 

 bark, and edgings to the depth of several feet. Flying about over 

 this area and alighting on the projecting sticks were swarms of Libel- 

 Inla quadrhnaculata Linnaeus, sometimes a dozen or more on the 

 same stick, and with them were numerous specimens of Argia tibialis 

 (Rambur), particularly along some piles of old slabs back from the 

 water. The most careful search revealed only three other species, 

 and in such small numbers that they could only be regarded as 

 stragglers. 



C. A third colony was found in Horseshoe Lake, a part of the 

 river surrounded on three sides by islands and opposite the town of 

 McGregor, Iowa. This was a colon}^ of Perifhemis domitia (Drury), 

 and Eincordxdia piineeps (Hagen), the former flying over the lily 

 pads by the score, the latter patrolling the pickerel weeds and rushes 

 a-long the shore. The only other dragonfly seen after long and care- 

 ful search was Llhellula pulcTiella Drur}^, which had evidently come 

 across from the mainland. 



D. Special mention should also be made of the two colonies of 

 Erythemis simpUcicollis (Say) observed on the Illinois River, one 



