482 The Naturalist Brazilian Expedition, Dy, 
In their movements these Siluroids are very sluggish, and their 
scale-like armor seems to serve as a real protection against large 
predatory fishes and icthoyphagous birds. 
Before going further it will be well to cast a general glance at 
the physical features of Rio Grande do Sul. Except the sand- 
banks and swamps of the lake-region, and some low alluvial lands 
near the River Uruguay, it may be said that the whole province 
is hilly or mountainous. The chains cross each other at all 
angles, and it would be difficult, with our present knowledge, to 
describe them in detail. In general the land is higher towards 
the north, and the extreme northern part of the province prop- 
erly belongs to the great orographic system which lies between 
the Parana and the Atlantic. This region is essentially a table 
land, much broken and frequently obscured by chains of hills and 
mountains. Toward the ocean it is abruptly cut down, forming 
that great rocky wall known as the Serra Geral, Serra do Mar, ot 
Brazilian coast range; to the west it falls gradually, or in a sent 
of mountain terraces to the Paraná. Soon after entering thè 
province of Rio Grande do Sol the Serra Geral bends away © 
the west, leaving the sea; beyond this the highland edge may be 
traced in a great curve to the valley of the Uruguay, but it grad- 
ually loses its distinctive character; the table-land is cut up by 
many rivers, and its outlines are lost among ranges of hills and 
mountains. One of these ranges, parting from the Serra Gt, 
passes southward through the middle of the province, separating 
the tributaries of the Uruguay from the streams which flow wi | 
the Lagoa dos Patos and the Lagoa Mirim. 
Aside from these orographic features, the province is 
into two very distinct physical regions. The rugged n 
portion is generally covered with forest, heaviest on the ! 
and along the river-courses, but in the main continuous: 
3 
sometimes cold: from May to August, when frosts are 5-4 t 
and ice is sometimes formed; snow is almos at 
on the highest mountains. Though this region extends a iy 
places as far as S: lat. 31°, the plants and animals are fest 
tropical, resembling those of Rio de Janeiro; palms and : on the 
are abundant; monkeys and toucans are as com Tae 
Amazons; and brilliant blue Morpho butterflies, of age fn 
Heliconii remind the entomologist that he is sti 
