. The Danish Ingolf-expedition. Marine animals -- Arctic regions; Scientific expeditions; Arctic regions. HYDROIPA II 135 of the point. In the northern Srrtiilaria species, we find a general tendency towards spiral arrange- ment of the branches, together with an often very marked approach to unilateral arrangement of the hydrothecae. The spirally placed branches are secondarily ramified, often dichotomically, bnt in Scrtularia tenera irregularly pinnately. P'rom this then, it is in reality but a short step to Ilydrall- rnania. And finally, there is a certain amount of variation in the Scrtulnr
. The Danish Ingolf-expedition. Marine animals -- Arctic regions; Scientific expeditions; Arctic regions. HYDROIPA II 135 of the point. In the northern Srrtiilaria species, we find a general tendency towards spiral arrange- ment of the branches, together with an often very marked approach to unilateral arrangement of the hydrothecae. The spirally placed branches are secondarily ramified, often dichotomically, bnt in Scrtularia tenera irregularly pinnately. P'rom this then, it is in reality but a short step to Ilydrall- rnania. And finally, there is a certain amount of variation in the Scrtulnrin species, with regard to proportion between the two sinuses, which in some species may be characterised as of equal size. We have thus, as the last and most essential distinctive feature, the fact that the adcanline closing mem- brane in Hydrail Ilia )iia has a free distal part, whereas in Scrtularia^ this is reserved for the abcauline membrane. It may be doubtful whether these small differences should be regarded as of generic im- portance; for the present, however, I have found it most correct to follow Levinsen in distinguish- intj between the two genera. Hydrallmania falcata (Ivinne) Hincks. 1758 Sertularia falcata, Linne, Systema naturae, Ed. 10, p. 810. 1868 Hydrallmauia falcata, Hincks, A History of the Britirdi Hydroid Zooplntes, p. 273, Colonies with slender, .spiral, monosiphonic and segmented main stem, where internodium bears a branch. The branches form an open spiral about the stem, and are themselves regularly secondarily ramified pinnately; the main stem has a hydro- theca in the corner at the origin of the branch, or may in rare cases be altogether devoid of hydrothecse. Branches and brauchlets are segmented, the irregular internodia bear on the one side (the upper) a more or less close row of hydrothec^e, the opening part of which is turned out alternately to either side from the median plane of the branch. On young pinnate colonies the hydrotheCcC are imbedd
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