104 BULLETIN 15 7, U. S. NATIONAL MUSEUM 



usually about 4, inches above the grass tops. It is noticeably swifter 

 than the smaller form found about Boston, which flies at the rate of 

 between 4 and 5 miles an hour. 



It is very unsuspicious, and if feeding on a flower may always be 

 captured with the greatest ease. It will sometimes alight on a flower 

 within a few inches of the collector. If frightened when on the wing, 

 as by the -close passage of a net, it usually closes the wings over the 

 back and drops into the grass, where it conceals itself, often quite 

 effectively. More rarely it makes off with increased speed in a 

 zigzag flight, but without rising above the usual height. This last 

 peculiarity is probably due to its fear of dragonflies, wdiich infest its 

 habitat in great numbers. Their plane of flight is higher than that 

 of the bog fritillaries, and although they quickly seize any unlucky 

 butterfly that rises to their level they will not pounce on anything 

 below them. 



Notes. — The specimens from Beltsville (pi. 3, figs. 5, 6; pi. 4, fig. 5) 

 are noticeably larger than specimens from the vicinity of Boston 

 (pi. 3, fig. 7). A series of 16 from Beltsville have the fore wings 

 from 22 mm. to 25 mm. in length, averaging 23.75 mm. A series of 

 19 taken at Dedham, Mass., on August 28, 1930, have the fore wings 

 from 18 mm. to 23 mm. long, averaging 20.3 mm. Mr. Scudder 

 gives the length of the fore wings in this species as from 17.5 mm. 

 to 21.5 mm., and the average as 20.6 mm. 



The ground color above is usually about the same as in the darkest 

 northern individuals, but in some it is darker and more reddish than 

 in ^ny from the north. The black markings are always somewhat 

 broader and heavier than in northern examples, and are often much 

 heavier so that they are more or less extensively confluent. On the 

 undersurface of the wings the color varies from about as dark as in 

 the darkest northej-n specimens to very appreciably richer. The 

 black markings on the underside of the fore wings are always heavier 

 than in northern examples. 



Genus ARGYNNIS Fabricius 



ARGYNNIS IDALIA (Drury) 



Regal Fkitillary 



Plate 13, Figures 1, 2 ; Plate 14, Figure 1 



Occurrence. — Common, but locally distributed, the males ranging 

 more widely than the females. This species is numerous in the 

 fields between Conduit Road and the canal beyond Cabin John and 

 in the damp hollows in the fields across Blair Road from the Hyslop 

 estate at Silver Spring, Md., frequent on the flats below Chain 

 Bridge, along the Eastern Branch, and in the bogs at Beltsville, and 



