Fifty-six species are described, including 15 new species of Candona and 1 of Eucypris. The morphology of male and female carapaces and some instars is considered. Pleistocene freshwater ostracods are abundant in slackwater deposits of North America. Candona is predominant in number of species as well as individuals, especially in deposits of cool alkaline water. Candona houghi, n. sp., C. swaini, n. sp., and C. cf. C. lactea developed into maturity in close proximity to glacial ice. The The ecologic interpretations for the Pleistocene assemblages and deposits agree in general with the interpretations of Recent assemblages by C. C. Hoff.