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It is possible to calculate the annual production of stream benthic animals from data obtained from a series of good quantitative samples collected at intervals during the year. The method is explained and its limitations and shortcomings are discussed. This seems at present to be the only simple and direct method of estimating production.

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Samples of the invertebrate fauna collected at ten points on a mountain stream in Trinidad reveal that the fauna is altitudinally zoned and that the apparent boundary between rhithron and potamon is below 30 m . This is very much lower than has previously been reported in the tropics .

In the light of findings in recent years about the extent and nature of the hyporheal zone, the rate of uptake of organic matter by stream beds, and the fact that groundwater contains dissolved organic matter, it is suggested that stream ecologists should learn much more than they now know about groundwater. It seems probable that it is an important source of organic matter to the stream ecosystem which has escaped consideration to date.

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