354 Natural History Bulletin. 



the shores of both river and lake, those along the river being 

 broader and of greater extent. On the side toward the inte- 

 rior of the mainland the heavy forests, which evidently once 

 covered the entire ridge, have been cleared away for some 

 distance to facilitate the defense of this important point in war. 



For several miles below San Carlos the shores of the San 

 Juan are low and swampy, and directly opposite and below 

 these marshes are very broad, and extend for several miles 

 along the south-east shore of the lake. Through these exten- 

 sive marshy fiats, which are made up of the silt brought down 

 by its own floods, the Rio Frio, a large stream having its 

 source in the distant mountains of Costa Rica, empties into 

 the lake from the south-east. Inasmuch as the San Juan flows 

 from the lake in almost exactly the opposite direction the two 

 streams are nearl}^ parallel for some distance, and near the lake 

 are separated only by a narrow swampy spit. These streams 

 are engaged in a constant struggle for mastery, the Rio Frio 

 persistently striving to close up the outlet of the lake, and the 

 San Juan equally persistently cutting its way through the 

 banks and bars of fine mud. The result is a gradual filling 

 up of the lake on this side, and unless the Rio Frio is turned 

 from its course (as it probably will be when the great canal is 

 completed) the lake shore will ultimately recede from San 

 Carlos leaving it an inland point. 



Because of the character of the surrounding country San 

 Carlos is an excellent locality for various swamp-species, but 

 for deep-forest collecting it is inferior to all the points along 

 the lower San Juan, It is an important localit}^ to the collector 

 however because it is from here alone that he can make ex- 

 cursions up the Rio Frio, along the east shore of the lake, or 

 across the lake to the more densely populated districts beyond. 



Three stops in all were made at San Carlos: the first from 

 December 3i3t to January 5th, the second on the nth of Feb- 

 ruary, and the third on a special trip made by the writer from 

 Castillo Viejo, March 12th. 



The first of these visits was made soon after the opening of 



