widespread species. Cottus rhotheus occurred at the most sampling sites, while C. beldingii showed the most restricted distribution. The distributions of C. perplexus and C. gulosus possessed interesting exclusions and overlaps suggesting keen competition. C. confusus was found only in streams with low summer temperatures. Of the seven primary species invading the lower Columbia River, five reach downstream to the influence of salt water. Only Mylocheilus caurinus and Catostomus macrocheilus are known to reside in brackish water. Richardsonius balteatus and Rhinich-
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Reimers et al. (1967) studied this question.