Three species of Hydractinia, H. allmani Bonnevie, H. carica Bergh and H. monocarpa Allman from the Arctic are redescribed from numerous colonies. The great differences noted between colonies of the same species are shown to depend on the stage of reproductive exhaustion reached when the colonies were taken. What is known of their biology and distribution is summarized. ON THREE NORTHERN SPECIES OF HYDRACTINIA This paper is confined to observations on three northern species, Hydractinia cdlmani Bonne vie, Hydractinia carica Bergh and Hydractinia monocarpa Allman, and is based on the rich arctic and subarctic collections of the Naturhistoriska Riksmuseum,Stockholm. Some of the material has been briefly described by Elof Jaderholm, but all the locality records of colonies in the Riksmuseum have been reported by him in various papers.

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The effect of live and dry diets on the growth and survival of cultured chub (Leuciscus cephalus) larvae was measured from 5 days post-hatch and over a 24 days period. At its conclusion, larvae fed artificial dry diets were significantly shorter, weighed less and suffered higher mortality rates than those fed Artemia and a mixed diet of Artemia spp. and a commercial feed.