2 BULLETIN 190, UNITED STATES NATIONAL MUSEUM 



and lb partly absorbed in a narrow longitudinal, elastic, downward fold 

 along the entire dorsal edge of the wing; this downward fold of the fore- 

 wing fits into a similar narrow upward fold along the costal edge of the 

 hindwing, both bearing a series of short, recurved spines, which interlock 

 and help further to keep the wings together. This structure (fig. la) of 

 the interlocking forewings and hindwings, first pointed out by Busck 

 (Proc. Ent. Soc. Washington, vol. 11, p. 115, 1909), is diagnostic of the 

 family Aegeriidae and is a most effective method of keeping the wings 

 together. 



In the hindwing, besides the specialized locking structure, the family 

 has retained the well-developed frenulum, normally a single strong spine 

 in both sexes, although occasionally females are found with a divided 

 frenulum. The hindwing is narrow but usually broader than the forewing, 

 with the costal edge straight, apex bluntly pointed, termen evenly rounded, 

 and normally with an indentation at vein Ic. The obscuring of veins 

 7 and 8 by the costal fold, as shown by Busck (loc. cit.), has caused earlier 

 workers to conclude in error that two veins were absent in the hindwing, 

 veins 8 and 5 (Meyrick) or veins 8 and 4 (Hampson), but if the wings 

 are softened and carefully denuded, all eight veins are found to be present. 

 Vein 2 from well before angle of cell ; 3 and 4 usually connate or stalked, 

 but 3 separate and before angle of cell in Paranihrene and other genera 

 and in Melittia nearer to 2 than to 4 ; 5 and 6 widely separated, parallel ; 

 6 from upper angle of cell ; 7 and 8 from base and partly obscured in the 

 fold or sometimes 7 out of 6 (Bembecia) ; the three anal veins normally 

 present and a partial fourth vein, stopping short between la and lb, is 

 often present. This vein has been given special attention by Spuler (Die 

 Schmetterlinge Europas, vol. 2, p. 311, 1910), who designated it "Bl" 

 and considered it of generic value in the genus Chamaesphecia Spuler. 

 From comparisons with hindwings of many other genera of the family 

 this vein seems to be merely a remnant of the basal fork of vein lb, which 

 in some genera is clearly defined and in others shows the gradual sepa- 

 ration and disintegration of the lower branch of the fork. This, however, 

 requires more study, especially of the pupal wings. John Henry Comstock 

 was the first to suggest that there actually may be four anal veins in 

 some of the groups of Aegeriidae {in Beutenmiiller, Menu Amer. Mus. 

 Nat. Hist., vol. 1, pt. 6, p. 221, 1901). 



The abdomen in the North American genera of the family is not con- 

 stricted at the base as it is in some exotic genera, only the genus Podosesia 

 having it somewhat constricted. The abdomen is smooth and in the male 

 is provided with a fan-shaped or wedge-shaped anal tuft; in several 

 genera there are long hair pencils (Sannina) or scaled processes 

 (Alcathoc) from the eighth segment. 



The legs, especially the hind ones, are variously modified, smooth or 

 hairy (Conopia), and sometimes tufted or spined at the tibial spurs. The 



