kinds of circumstances. (i) The resource is easy to find and profitable to extract right down to the very last member of the species (Vernon Smith gives the woolly mammoth as an example). Smith [5] and Gould [3] show how this comes about in a dynamic model and a static model, respectively. (ii) Although the cost structure of the exploiting industry usually protects the endangered species, a random shocksuch as the warm wind, El Nii-no, on the Peruvian anchovy-displaces the system from equilibrium, and then the immobile fixed capital in the industry relentlessly hunts down and captures the very last member of the species. The second scenario gives rise to a number of more or less restrictive models in which the necessary conditions for extinction have been adduced. In a more general model containing many of the previous models as a proper subset, it is shown that, except in unlikely circumstances, necessary conditions for the case (ii) type extinction are not described, as the previous authors have said, in terms of growth rates of the resource or returns-to-scale parameters; rather, the necessary conditions for