Packard.] 
492 
[Feb. 19, 
distinct, which appear at different seasons of the year, the one in 
early spring, the other in summer. To these forms Weismann, in 
his great work, “ Studies on the Theory of Descent,” gives the 
name of summer and winter form. Other European butterflies 
were found to be dimorphic, and several species in the United 
States by Mr. W. H. Edwards, and Dr. Speyer communicated to 
Weismann the fact that he had also found that two Geometrids, spe- 
cies of Selenia, are seasonably dimorphic, while Professor Meldola 
adds in the same footnote (p. 4), that Professor Westwood had 
found that two species of Ephyra were also dimorphic. 
What I have to state in regard to the seasonal dimorphism of 
the two species of Platyptericids above named is not the result of 
my own observations, but of those of the late Mr. S. Lowell El- 
liot, so well known for his success and skill in rearing Lepidoptera. 
In conversation in 1887, about a year before his death, Mr. 
Elliot told me, and I took notes at the time, that Drepana arcuata 
Walk, and D. genicula (Grote) were the same species, but belonged 
to different broods ; that D. genicula comes from the first of J une 
and early July brood of caterpillars, and D. arcuata from the sec- 
ond. He also gave me specimens of the two forms, and I noted 
the fact on the label of each that D. arcuata came from a pupa 
which had hibernated, and D. genicula from a summer pupa. Mr. 
Elliot also added that a part of the brood of D. arcuata appears 
in the autumn, and a part hibernate, and he told me also that some 
of the chrysalids of D. genicula hibernate. 
Having found D. arcuata both in Massachusetts and in northern 
New York in June, I am inclined to believe that the species, D. 
arcuata , is seasonally dimorphic, and that D. genicula , heretofore 
regarded as a good species, is simply the summer form of D. arcu- 
ata. The larvae of the two forms appear to be the same. 
Comparing the males, D. arcuata is the paler, with much paler 
hind wings, and is generally, if not always, of larger size. D. 
genicula , which I have determined from Grote’s description, figure 
and type, differs in the following points : the markings and their 
arrangement are the same, but the ground color of the summer 
form (| genicula ;) is much deeper in tone ; the fore wings being a 
shade darker and deeper and more uniformly brown, while the 
hind wings are yellow-oclireous rather than whitisli-ochreous as 
in the winter form (arcuata), and both wings beneath are deeper 
oclireous. The lines and other dark markings are, owing to the 
