1904] FIELD: — BAS/LARCHIA 5 



V. Proserpina Considered as a Possible Hybrid. 



Scudder ('89) treats proserpina as a hybrid produced by the crossing of 

 arthemis and astyanax. The principal facts upon which he bases his theory are : 



1. The occurrence of apparent hybrids arthemis-archippus and astyanax- 

 archippus. 



2. Proserpina resembles astyanax even more closely than arthemis, to which 

 latter species Edwards has proved it to be in some way related. 



3. In structure of gemizWdi proserpina and astyanax are precisely alike. 



4. Proserpina is more variable than either of the supposed parents. 



5. Proserpina occurs only in a narrow belt where the ranges of its supposed 

 parents overlap. 



6. ^'■Proserpina is known at so many points in this belt, that it presumably 

 occurs wherever arthemis and astyanax are brought into contact." 



7. No dimorphic species is known of which one of the forms appears only 

 along one edge of the territory occupied by the species. 



VI. The Facts Summarized. 



The three recognized species, Basilarchia arthemis, B. astyanax and B. archtp- 

 pus, all occur together in a narrow zone running westward from the Atlantic coast to 

 the Mississippi river ; north of that zone, arthemis and archippus occur together ; 

 south of it, astyanax and archippus occur together. 



With these three species we may effect three different combinations of two 

 species each, viz.: arthemis-archippus , arthemis-astyanax, archippus-astyanax. 



Each of these three combinations is actually represented by an intermediate 

 form. 



Two of these intermediate forms, arthemis-archippus and archippus-astyanax, 

 are generally believed to be hybrids, but their hybrid nature is as yet undemon- 

 strated. 



The third, arthemis-astyanax, is really a group of several interblending forms, 

 assembled under the name proserpina. 



The proserpina forms are either the results of the intercrossing of arthemis and 

 astyanax, or polymorphic forms of arthemis} They are found in the narrow zone 

 above mentioned. 



1 Grey ('79) has suggested that the three supposed species are polymorphic forms of one species. The statement here 

 given does not necessarily preclude the view that astyanax and arthemis may both be forms of a single polymorphic spe- 

 cies. Mr. H. H. Newcomb has suggested this to the Cambridge Entomological Club. 



