Abstract

Many of the resemblances, both conspicuous and subtle, noted among North American crayfishes should not be interpreted as indicative of kinship. Just as albinism among the troglobitic species is a reflection of the environment in which the animals live, so is the depressed, broad chela with an excised dactyl indicative of the burrowing propensity of the owner; also, the areola width is, to some extent, a measure of the relative degree of saturation of oxygen in the water in which the crayfish is living. There is evidence that other similarities that have not been correlated with environmental conditions have also been independently acquired in different crayfish stocks. Outstanding among these are the dispositions of the terminal elements of the first pleopods of the males of Cambarus, Fallicambarus, and Hobbseus. Similarly, the presence of hooks on the ischia of the third, fourth and fifth pereiopods in males occurs in such combinations in different stocks that similarities must at least occasionally have been reached through convergence. As a result of some of these similarities that are believed to have been so derived, several students of crayfish phylogeny have been misled in using them in assessing the interrelationships of the American crayfishes and have erred in proposing species groups based upon certain of these independently acquired characteristics.

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