8 BULLETIN 15 7, U. S. NATIONAL MUSEUM 



The greater part of Mr. Scudder's material came from the vicinity 

 of Salem and Cambridge, Mass. The use of his work as a standard 

 in the present study was therefore supplemented by my assembling a 

 collection of several thousand specimens from Manchester and Essex, 

 Mass., near Salem, and from Newton, Mass., near Cambridge. In the 

 course of this work some wholly unexpected captures were made, 

 which have been recorded elsewhere. It may be remarked that it is 

 far easier to assemble satisfactory series of local butterflies in eastern 

 Massachusetts than it is in the vicinity of the District. 



To the use of Mr. Scudder's descriptions as standards the objection 

 might be raised that as they are based almost entirely on specimens 

 from the transition zone between the southern and Canadian forms 

 they represent neither the one nor the other and are therefore mis- 

 leading. The answer to this is that in practically all cases the 

 Canadian forms show a gradual change westward and especially 

 northward from northern New England, while the southern forms 

 similarly show a gradual change from southern New England and 

 New York southward. Mr. Scudder's descriptions furnish a fixed 

 point from which to work, and this is the main requisite. 



Theoretically the form occurring in the type locality should be 

 redescribed and considered as the standard for each species. But 

 this procedure is not practicable. In a few cases the type locality 

 is in the Canadian area, in many it is in the transition zone, and in 

 many it is in widely varying places in the southern area. Another 

 difficulty is that names based upon specimens from the transition 

 zone are often of very doubtful application except as regards the 

 species as a whole. For while some species pass by a series of minute 

 intergradations from one geographical form to another, others do 

 not, the northern and southern forms occurring together with few 

 or no intergrades, or with one or perhaps two well-marked inter- 

 grading types. 



Many District butterflies occur locally in two or more different 

 forms. Eight common species have two or more broods a year with 

 the first brood emerging from the pupae over a period of several 

 weeks beginning very early in the spring — late in March or early 

 in April. 



These eight species are: The pearl crescent {Phyciodes tharos)^ 

 the common blue {Lycaenopsis argiolus psevdargiolus) , the checkered 

 white {Pieris frotodice)^ the cabbage butterfly {Pieris rapae), the 

 yellow clover {C olios phUodice), the blue swallowtail {Papilio 

 philenor), the yellow swallowtail {Papilio glaucus), and the zebra 

 swallowtail {Papilio ruarcellus) . 



All these butterflies have two different forms in spring and 

 still a third form in summer. The earliest individuals to appear are 

 of a distinctive type. These later are rather suddenly replaced by 



