CATALOGUE OF BTJTTEEFLIES. 3 



there was no wind to ruffle the surface. One or two of the more 

 observant had noticed that the Eutterflies lit on the surface of 

 the water, rested there for a little while, and then rose again and 

 pursued their flight. From what I could make out of the extent 

 of the column, I estimated that the denser portion was about 

 one hundred yards wide, but that the stragglers on either side 

 extended very much further. The length of it must have been 

 very great, for though they did not seem to advance beyond from 

 about two to three miles an hour, yet even the denser portion of 

 the swarm was quite four hours in passing, and had not com- 

 menced to decrease in numbers when the storm dispersed them. 

 It seems impossible to form any estimate of their immense num- 

 bers, but, however incredible it may appear, there must have 

 been millions of them. Where they came from is a very puzzling 

 question, and unless they travelled across the sea at a much 

 quicker rate, they would require several days to cross from the 

 nearest part of the continent. It seems difficult to believe they 

 could accomplish this, yet there can be no doubt that an Ameri- 

 can Butterfly, Anosia plexippus^ has more than once crossed the 

 Atlantic and reached our shores in considerable numbers. The 

 specimens of Brassicce which I secured from this swarm were 

 all in very fine condition and of unusual size. 



I am of opinion that a very large immigration of this and the 

 following species took place in the autumn of 1887, for both of 

 them appeared suddenly in this neighbourhood in enormous 

 numbers, but no one, that I am aware of, observed them in 

 passage. 



2. P. Rapae (Linn.). Small White. 



F. Rapce, Staint. Man., vol. 1, p. 18. 

 „ Kewm. B. B., p. 161. 



„ Barrett's Lep. Brit. Is., vol. 1, p. 23. 



Larva. Buck., vol. 1, pi. ii., fig. 3 ; Wilson, pi. 1, fig. 4. 



Equally, or even more common than the last species. The 

 larva is rather more general in its food, feeding on various 



