. The Danish Ingolf-Expedition. Scientific expeditions; Arctic Ocean. theca can vary with regard to curvature, and may in extreme cases somewhat resemble Halecium labrosum; in Halecium muricatum however, we always find that the adcauline margin of the hydro- theca is more markedly curved, the abcauline less so. Normally, the length of the interuodium is about three times its distal breadth (including the apophyse); we have, however, from the "Ingolf" St 125, a colony which, from its extremely long inter- nodia, must be regarded as a deep-sea variant (fig. XVII b\ forma abyssalis nov.
. The Danish Ingolf-Expedition. Scientific expeditions; Arctic Ocean. theca can vary with regard to curvature, and may in extreme cases somewhat resemble Halecium labrosum; in Halecium muricatum however, we always find that the adcauline margin of the hydro- theca is more markedly curved, the abcauline less so. Normally, the length of the interuodium is about three times its distal breadth (including the apophyse); we have, however, from the "Ingolf" St 125, a colony which, from its extremely long inter- nodia, must be regarded as a deep-sea variant (fig. XVII b\ forma abyssalis nov. It is not unusual among hydroids to find that the colonies from greater depths exhibit an extension of the single branch parts; in this case, however, the tendency is pushed to an extreme, and at a first glance, the colony presents an altogether alien appearance. It is probably clue to the fact that the species here occurs in the cold area, at the considerable depth of 729 fathoms. The colonies are very slender, about 10 cm high, with polysiphonic stems. The internodia of the minor branches are 3—4 mm long, about five times the distal breadth incl. apophyse. The apophyse itself is very distinctly mar- ked and bears a slender hydrotheca. The hydrotheca has close under the diaphragm the typical adcauline thick- ening of the wall, the "pseudodia- phragm" which as a rule is also found in the typical form. The hvdrothecae Fig XVII a_b exhibit the form typical for the spe- Halecium muricatum. ,, , , , ., a. Internodium and hvdrothecae cies; the secondary hvdrothecae are from a typical colony from Store comparatively short-stalked, but other- Hellefiskebanke, depth 32 fath. wise of the same shape as the pri- j. Internodium with hydrothecaa mary. The colonies are sterile. From of forma «*?««** from "ingolf St. 125. (X 401. * the features mentioned it follows that the colonies cannot be taken as representatives of a distinct species; they should, however, be distin-
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