HYDROIDA 11 ji: 



disappearance of the blind sack as a secondar>- phenomenon, and keeps mainly to the character of 

 the gonangia. In this, ho\ve\-er, it is impossible to concur, as these organisational featnres are entirel\- 

 independent one of another, and the lines of development in gonangia and jjolvps can clearh- 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; phylogeneticalh', it is the most valuable clue. And 

 in this case, it suggests that lid formation ma\' parth' indicate converging lines, as will be seen from 

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

 Levinsen in grouping Dxiiaiiiciia and Scrtiilaria together in one genus exclusively from the uni- 

 formity of their closing apparatus. 



Dynamena pumila (Linnei I^amourou.\. 

 1758 Sertitlaria puii/i/a, Linne, Systema naturce, Ed. 10, p. 807. 

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



Upright colonies with irregular, as a rule pinnate ramification, exceptionall\' with an indication 

 of nionosiphonic main stem. The branches are secondarily ramified in irregular pinnate formation. 

 The colony is divided into short internodia, each bearing a pair of hydrothecse oppositely placed. The 

 hydrotheca is deepl\- 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 slightlv 

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

 large, with a free distal part. The diaphragm almost radialh- sxinmetrical. 



The gonothecce proceed from below the base of the Indrothecre on the one side of the branches. Tlie\- 

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

 Material : 



Greenland: Egedesminde 

 vSukkertoppen 

 Julianehaab, on Fitcns. 

 Kangerdluarsuanguak. 

 Iceland: Reykjavik, on Ascophylliini, and Fitcits^ 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 

 gouotheca (1904 p. 27, fig. 80) is altogether misleading, presenting the impression that the acrocy.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 pttiiiita belongs to the tidal zone, and is most frequentl)- found on fucoids and the 

 shallower living Laininaria\ the species evinces a high degree of elasticitv with regard to salinity, 



