358 L. de Nic6ville & Dr. L. Martin— Baltei'jlies of Sumatra. [No. 3, 
ancl western borders of these sultanates are formed by the Barisans, 
here named the Battak mountains from the inhabitants of these ranges 
being several tribes of anthropophagous Battaks, the aborigines of 
Sumatra. The different ranges of the Battak mountains here include 
the extensive Toba highlands, which surround the large and for long 
mysterious Lake Toba that lies in their centre. North of this lake 
is the Karo plateau, inhabited by the Karo-Battak tribe, and forming 
the true “ hinter-land ” of the above-named sultanates. The northern 
boundary of this region — as we deal chiefly with this part of the island, 
we will call it “our area”—is the mountainous land of the Gayoe 
and Allas tribes, who are Mahomedans; to the east lies the large 
sultanate of Siak. The altitude of the Karo plateau may be estimated 
at about 4,000 feet; the highest peaks of the Battak mountains are 
Simanabum, nearly 8,000 feet in height, and Sebayak, which is a little 
over 7,000 feet. 
Owing to its situation, protected on the south and west by the 
Barisans, and with the narrow and quiet Strait of Malacca, beyond 
which again is the Malay Peninsula also with a high central range 
to the north and east, there is no monsoon in our area, and consequently 
neither a true rainy, nor a true dry season; though during the 
south-west monsoon there is a little more rain than usual, say about 
18 days in the month, while during the north-east monsoon there are 
only 11 rainy days in the month. Nevertheless there is a yearly average 
rainfall of about 90 inches (2,200 mm.) ; this, together with a 
mean daily temperature of 80°, and an extreme daily range of 126° 
Fahrenheit, makes a very damp and unhealthy climate, but fits it for a 
high development of insect life. The plains of the three sultanates, 
the outer ranges of the Battak mountains, and the Battak mountains 
themselves, which include the Karo Central Plateau, are the localities 
where all the species of Rhopalocera contained in our collections and 
enumerated in the following list, have been captured, except a few 
from the Gayoe lands and from Indragiri, another Malayan sultanate 
south of Siak, and nearly opposite to Singapore. 
The plains were formerly entirely covered with large, dense, lofty 
primeval forest, but this has had to make way for the miserable tobacco 
plant, of which the cultivation began about the year 1865. Tliq 
primeval forest once destroyed by fire and the axe does not grow again, 
but is replaced by a high-growing and tenacious species of grass, 
called “ Lalang ” in Malay (Imjperata arundinacea , Cyrill.), which 
now entirely covers all the ground temporarily unoccupied by tobacco. 
The cultivation of the nicotin'ous plant pays so highly and yearly 
so increases in extent, that there is now no forest whatever left in the 
