HYDROIDA II 



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disappearance of the blind sack as a secondary phenomenon, and keeps mainly to the character of 

 the gonangia. In this, however, it is impossible to concur, as these organisational features are entirely 

 independent one of another, and the lines of development in gonangia and polyps can clearly not be- 

 taken as of equal significance. There is, as I have often here pointed out, no reason to reduce the 

 importance of polyp development in systematics; phylogenetically, it is the most valuable clue. And 

 in this case, it suggests that lid formation may partly indicate converging lines, as will be seen from 

 the diagram given under the heading of Sertulariidce. It is therefore likewise impossible to follow 

 Levinsen in grouping Dynamena and Sertularia together in one genus exclusively from the uni- 

 formity of their closing apparatus. 



Dynamena pumila (Linne i Lamouroux. 

 1758 Sertularia pumila^ Linne, Systema naturae, Ed. 10. p. 807. 

 1812 Dynamena pumila. Lamouroux, Extrait d'une memoire sur la classification des Polypes, p. 184. 



Upright colonies with irregular, as a rule pinnate ramification, exceptionally with an indication 

 of monosiphonic main stem. The branches are secondarilv ramified in irregular pinnate formation. 

 The colon)- is divided into short internodia, each bearing a pair of hydrotheca; oppositely placed. The 

 hydrotheca is deeply embedded ; its adcauline wall has a free distal portion about the same length as 

 the opening diameter, between one-fourth and one-third the length of the hydrotheca. The opening 

 margin has two prominent lateral teeth, and in the middle of the adcauline lesser sinus is a slightly 

 developed broad median tooth. The adcauline closing membrane has no free part; the abcauline is 

 large, with a free distal part. The diaphragm almost radially symmetrical. 



The gonothecae proceed from below the base of the hydrothecse on the one side of the branches. They 

 are pear-shaped, with a very short neck, and a round, symmetrically situate distal opening with operculum. 

 Material: 



Greenland: Egedesminde 

 Sukkertoppen 

 Julianehaab, on Fucus. 

 Kangerdluarsuanguak. 

 Iceland: Reykjavik, on Ascophylhtui, and Fucus, and down to 4 fathoms depth. 

 Grindavik, Bredebugt 

 Grafarvogr 

 Isafjord. 

 The Faroe Islands: Stromo. 



Thorshavn. 

 I have in a former work (Broch 1910 p.- 29) pointed out that Nutting's drawing of the 

 gonotheca (1904 p. 27, fig. 80) is altogether misleading, presenting the impression that the acroc\ st, 

 as it projects from the gonotheca, must perforate the operculum. This is, however, not the case; the 

 operculum opens at one side, and the acrocyst is then thrust through the opening thus made. 



Dynamena pumila belongs to the tidal zone, and is most frequently found on fucoids and the 

 shallower living Laminaria\ the species evinces a high degree of elasticity with regard to salinity, 



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