Cljt (fonarjian (KirtpraolopL 



VOL. XX. LONDON, NOVEMBER, 1888. No. 11. 



AN EXTREME CASE OF SEASONAL DIMORPHISM IN COLIAS. 



BV T. D. A. COCKERELL, WEST CLIFF, COLORADO. 



It was thought strange when it was proved that Colias keewaydin and 

 C. eurytheme were seasonal forms of a single species Still stranger did 

 it seem when Mr. W. H. Edwards proved by breeding that C. eriphyle 

 (alias Hagenii) was also a form of eurytheme, but even after this I was 

 not quite prepared for the conclusion, forced upon me by irresistible 

 facts, that in this locality the orange and yellow forms were not only of 

 one species, but actually alternated seasonally, the former being the 

 summer, and the latter the winter form. The locality in question is the 

 eastern slope of the Sangre de Cristo range, in Custer County, Colorado, 

 in the neighborhood of Swift Creek, at altitudes varying from about 7,800 

 to 8,400 feet. Only two forms of C. eurytheme are found (exclusive of 

 the pale females), and neither of these agrees precisely with those already 

 described, so that ("West American Scientist," 1888, p. 42,) I called the 

 orange one intermedia, and the sulphur yellow form autumnalis, this last 

 being very close to C. eriphyle. 



The facts of the case are best shown by extracts from my diary, all 

 bearing upon this locality : — 



July 13th, 1887. — Arrived here, found intermedia flying abundantly, and 

 so until the middle of August, when I left for a trip to the western 

 slope. No autumnalis seen. 



October 22nd. — Returned to this locality ; a few worn intermedia seen, 

 the last of brood. 



November 9th. — Caught a % autumnalis, the first I had seen. 



May 13th, 1888. — Caught a % autumnalis — the first of the year. Soon 

 after autumnalis became common, but no intermedia seen. The first 

 £ was caught May 19th. (The $ 's of both forms of eurytheme, and 

 also of C. alexandra, seem to emerge here sooner than the £'s.) 



June 4th. — The first intermedia of the year seen. 



