FEB -23 1904 



PSYCH K. 



PROBLEMS IN THE GENUS BASILARCHIA. Plates I-III. 



BY W. L. W. FIELD, MILTON, MASS. 



I. Introduction. 



Among the representatives of the genus Basilarchia occurring in the north- 

 eastern United States are certain remarkable forms which seem in a measure to 

 bridge the gaps between the three types to which specific rank has been generally 

 accorded. Some of these intermediate forms have been figured and described as 

 probable hybrids, others as aberrant or dimorphic forms; several others are known 

 to which no distinct names have been given. This paper is the result of an effort 

 to summarize the existing knowledge of these forms, in order to prepare the way 

 for methodical investigation. 



II. The Three Generally Recognized Species. 



No attempt will be made here to present detailed descriptions of these familiar 

 butterflies, which are treated in all the leading works on North American lepidop- 

 tera. It will suffice to point out certain pertinent facts. 



1. B. arthemis Drury (Plate I., fig. 5, $ ; Plate II., fig. 4, J* ) , the common 

 white-banded species of the mountain districts, ranges very widely through Canada, 

 and in the United States frequents northern New England, the Adirondack and 

 Catskill regions, and a belt of country extending westward to Minnesota. About 

 Boston it is very rare, but has been taken by Harris, Clapp, Miss Guild, Morse, 

 F. H. Sprague, P. S. Sprague, Zerrahn and others. Reported instances of its 

 capture south of the latitude of Boston are so scarce as to emphasize its almost 

 complete restriction to the hilly country of the north. The species is reported 

 from most stations either as single-brooded or as having a partial second brood. 

 The larvae feed upon poplar and willow. 



2. B. astyanax Fab. (Plate I., fig. i, $\ fig. 2, 9 ), the blue-black species 

 without white band, is absent from Canada with the exception of southern Ontario, 

 and even in the United States encroaches very little upon the territory of arthemis. 

 In general it may be said that astyanax seldom appears north of latitude 43°, but 

 that south of latitude 42° it replaces arthemis. It is found as far west as the 



