Mr, C. B. Williams' Notes on Butterfly Migrations 155 



to April is more or less dry ; May to the middle of August 

 wet ; the end of August to October the driest season ; 

 and November to February again wet. Further in the 

 interior the second dry season is lost, and there is only 

 one wet and one dry season each year. 



There are given below particulars of sixteen different 

 migrations (really more, as some of the records refer to a 

 number of similar migrations seen in the same locality in 

 different years). All except one of these refer to Callidryas 

 eubule. Two are from my own observations, nine are 

 collected from residents and are, I believe, quite reliable, 

 while five have been previously recorded. The exact 

 locality and direction of all, except one, will be found 

 indicated on the accompanying map. 



1. This migration I saw in the North-west District of 

 British Guiana within a short distance of the Venezuelan 

 border. Most of the observations were made on the River 

 Aruka, between the junction with the Barima, of which it 

 is a tributary, and Issororo about six miles further up the 

 Aruka. The junction of the two rivers is about twelve 

 miles in a direct line to the coast, and about nine miles from 

 Venezuela. The district is chiefly a vast forest swamp, 

 below the high-tide sea level, with here and there a small 

 rounded or flat-topped hill, one or two hundred feet high. 



The migration consisted almost entirely of the yellow 

 Pierid Callidryas eubide, interspersed with a very small 

 proportion of at least three other species which I was 

 unable to catch; one of them, a large, dark, Papilio-like 

 insect, may possibly have been Cydimon \TJranid\ leilus, 

 a day-flying moth which is not uncommon in the district, 

 and which has been recorded as having migrations of its 

 own. 



I first became aware of the migration on Augvist 1st, 

 1916, although three days before specimens had been 

 noticed in the district. It was then two and a half months 

 after the beginning of the first wet season. The migration 

 was only at times really conspicuous and never attained 

 a density which could without exaggeration be recorded 

 as a " thick cloud." On many days only careful observa- 

 tion indicated that anything unusual was occurring. In 

 order to get a comparative idea of the density of the 

 migration a distance of about two hundred yards was 

 estimated from the observer in a line across the direction 

 of flight (in close spaces this sometimes had to be reduced 



