HYDROIDA II 



97 



the species, with the marsupial chamber resembling that of Diphasia fallax (Johnston) and Diphasia 

 rosacca (Linne) have led to its being frequently referred to this genus. The state of the material 

 did not permit of a quite certain investigation of the polyps, but as far as it was possible to judge 

 it has a quite rudimentary blind sack, which brings the species nearer to Diphasia. On the other 

 hand, the closing apparatus is altogether of the same type as Sertularella, thus removing the species 

 again from Diphasia. The most natural thing would doubtless be to consider Sertularella tamarisca 

 as the type of a distinct genus, which in a certain degree forms a link between the true Sertularia 

 species and Diphasia. This would demand, however, in the first place a closer study of the structural 



... . _.. 2 ooo m. 



20o m. .. 6 oo m. ._ looom. 



Fig. LI. The distribution of Sertularella tamarisca in the Northern Atlantic. 

 In the hatched regions the literature notes a scattered occurrence without giving particular data. 



conditions of the species, and as my material is not suited to the purposes of such investigation, I 

 have for the present refrained from establishing the new genus here. 



It is not altogether easy to determine with certainty the biogeographical character of the 

 species. Sertularella tamarisca is not a form of frequent occurrence, and is never met with in large 

 numbers at a time; on the contrary, it is as a rule taken in single specimens, so that the species 

 appears to be somewhat of a rarity. Further study seems to show that it is a boreal species capable 

 of penetrating slightly into the arctic area and even more into warmer waters. Towards the north, 

 it comes up into the White Sea, and towards the south, as we know, it penetrates into the Mediter- 

 ranean. In the waters investigated (fig. LI) the species has not infrequently been found in the eastern 

 part of the boreal region, while it has only once been met with in Davis Strait; it never penetrates 

 into the cold area, despite the fact that its wide bathymetrical range would seem to suggest a con- 



The Ingolf-Expedition. V. 7. 



