IQ BULLETIN 15 7, U. S. NATIONAL MUSEUM 



forms, and the early-spring and comparable forms are primarily dry 

 forms, usually showing to a greater or lesser degree the influence 



of cold. 



Spring and autumn are seasons of cool nights and warm or even 

 hot days. The heating of the air during the day reduces the amount 

 of contained water vapor far below the saturation point. This might 

 be expected to result in the appearance of dry butterflies resembling 

 those appearing in subarctic regions under essentially the same 

 conditions, and corresponding to others appearing in unusually dry 

 summers or in unusually dry regions. 



In addition to these normal forms of butterflies, individuals occur 

 in every species which are more or less widely different from the 

 usual type. These so-called aberrations may be quite erratic, or 

 they may appear more or less regularly. Very few of them have 

 been found in the District; of those which are known from this 

 region the two most noteworthy are Papilio troilus ab. radiatus and 

 Euphydryas phaeton ab. superhus. 



From time to time butterflies are found in which both sexes are 

 combined in a single individual. One side may be male and the 

 other female, as in a specimen of Atalopedes campestris recorded 

 and figured herein (pi. 16, fig. 3), or the two sexes may be mixed in 

 a more or less haphazard way; for instance, one or more of the 

 wings may show patches of both the male and female color pattern. 



It has become rather a popular diversion to bestow special names 

 on the various forms of each butterfly, and even upon the aberra- 

 tions. I can not see that this procedure helps in any way to clarify 

 the subject — on the contrary, it often tends to obscure it. For in- 

 stance, the yellow swallowtail {Papilio glaucus) is usually supposed 

 to have one yellow and one black female form, chiefly because one 

 of the yellow and one of the black female forms have received 

 names. As a matter of fact, it has a whole series of female forms 

 ranging from cream-white to black, while the spring black female 

 is distinguishable at a glance from the summer black female. Some 

 of these female forms are stable and some are very variable, inter- 

 grading imperceptibly into others. Giving names to them implies 

 a certain fixity of type that in reality does not exist and therefore 

 conveys a false idea of their significance. 



In the following pages wherever special names have been given 

 to seasonal or other forms they are usually mentioned, but no new 

 names are applied, and no new names are given to aberrations. 



NOMENCLATURE 



In a preliminary list of the butterflies of the District published in 

 connection with the present memoir, the nomenclature adopted was 



