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conical pits of ant lions often covered the ground so thickly that it was impossible to avoid walking on them.

Once near the sea we came across a great number of terrestrial hermit crabs, Cenobita diogenes, each encased in the shell of a land snail. The little army was moving slowly through a rocky portion of the desert where its members could sidle quickly from the shelter of one rock to that of another. These little crabs live a truly terrestrial life, and return to the ocean only once a year, when they breed. They apparently require very little water, for I brought three home with me and they have lived in a dish of dry sand in my office for more than six months. They have of course been supplied with food and a small cup of drinking water.

This desert, like those in other parts of the world, has a rather sparse fauna consisting of a few species, most of which are able to stand extreme desiccation, long fasts and great heat. The lizards and tortoises with their dry, scaly skins, the land hermits with thick exoskeletons and borrowed shells, the land snails with thick calcareous coverings, are all admirably suited to desert conditions.

The streams on the northern Colombian coastal slope are easily divisible into two classes—mountain torrents and rather slow-flowing meandering rivers. From headwaters in the mountains the water rushes down over rocky beds for a time, then comes abruptly to the level sandy plain where much of its impetus is soon lost.

The most striking characteristic of the animals of the mountain torrents is their ability to hold on. The little catfish found there have a