1891.] W. Doherty — A List of the Butterflies of Engano. 
5 
heaval occurred, its place was probably occupied by a few isolated is- 
lets, and to this day its fauna is chiefly made up of immigrants from the 
Malay Peninsula, and in the extreme south-west from Java, the number 
of endemic species being small. To understand the faunal relations of 
the Nias Islands, one must eliminate all idea of Sumatra from the mind. 
Until quite recent times, their relations were, I think, wholly with Java 
on the one side and the Nicobars on the other. 
The Nias Islands lie like a broken breakwater along the western 
coast of Sumatra, in a line between five and six hundred miles in length, 
from Pulo Babi to South Pageh. They are separated from Sumatra by 
a deep channel nearly a hundred miles in breadth, but in two places 
more or less bridged by islands. Their united area is now only about 
6000 square miles, equal to that of Yorkshire. But they seem to be the 
remains of a much larger mass of land. The deep sea that surrounds 
them swallows up all the alluvium from their streams; the tremendous 
surf on their western shore steadily undermines their hills, and under 
this process the islands have long been wearing away. 
Engano lies much further south, and is wholly surrounded by deep 
sea, in which it might long ago have disappeared but for the coral reefs 
that protect most of its coast. It is only eighty miles from Sumatra, to 
which it has no faunal resemblance whatever. On the other hand, it is 
180 miles from South Pageh in the Nias group, and 210 from Java. But 
on the side of Java there is only open sea, while on that of Nias there 
are three or four reefs and islets, and as might bo expected from this, 
Engano may be zoologically considered as as an outlying member of the 
Nias group, with certain Javan affinities. 
An excellent description of the people and products of Engano has 
lately appeared in the Tijdschrift van Nederlandsch Indie, but so little 
is said of the island itself, that I may be permitted a few remarks on the 
subject. The area seems to be incorrectly stated ; it is about a hundred 
and twenty square miles. The eastern coast is low and flat, bordered in 
places by mangrove swamps. The western, where the hills attain a 
height of nearly a thousand feet, descends precipitously into a 
narrow lagoon filled with branching corals and coral-haunting fishes, 
and on the reef beyond, the surf of one of the bluest and deepest of seas 
beats continually with such violence that the whole island seems to 
shake under it. Engano seems now to be sinking ; it has formerly been 
more or less submerged. A shell of coral rock covers almost the whole 
of it, thick over the eastern lowlands, thinning gradually to the west- 
ward, so that the streams generally break through it there, and flow 
through deep gorges. In some places the crust has given way so as to 
form deep little round dells, with stalactite caves piercing their sides, 
