4 University of Michigan 
B. Aquatic Habitats. 
V. Lowland forest ponds. Swamps and pools, mainly tem- 
porary, in the forest itself and in the cleared regions. ‘The 
two main classes studied are: (a) pool-swamps in the low 
jungle along La Laja; and (b) the pools in the burnt-over 
region and cleared land. 
VI. Savannah ponds. Established ponds in the savannahs. 
Although the Laguna de Chacalapa is about a mile in length, 
it is not over a meter deep at the height of the wet season. 
Only one shell was obtained. 
VII. Rivers and lakes. a. La Laja. This is what is known 
in many Spanish-American countries as a camo (literally, a 
sewer). It is a sluggish stream and black-water channel off 
of the Arroyo Hueyapam, and does credit to its Spanish — 
designation. 
b. Sand-bars of the Arroyo Hueyapam. At the hacienda, 
the Hueyapam consists of a steep-banked channel about fifty 
yards by twenty to thirty feet deep, which, dependent upon 
the weather, may contain anything from a sizable creek, with 
pools, little rapids and sand-bars, to a raging torrent that com- 
pletely fills or overflows it. It is quite typical of the scoured, 
sandy creeks so common in the tropics. 
c. Rio San Juan. A quite large river, which was in flood at 
the time visited, and in some places over-reached its banks for 
almost half a mile. Its bottom is probably sandy. 
d. Laguna de Catemaco. A deep-basined crater (?) lake, 
several miles in diameter. Most of the shore is of volcanic 
rock and it contained several rocky islands, but near the out- 
let and in some other places this is covered by a deposit of 
humus-material. The latter developed, in some parts, a mag- 
nificent border of water-hyacinths, a hundred yards wide or 
more. Collecting was also done in a small, but very deep, body 
