HYDROIDA 21 



from the "Michael Sars" 1902, when the species was found in the warm Atlantic waters to the south of the 

 Wyville-Thomson-Ridge (Brocli 1903). There is in this case a possibility that the animal has been carried 

 witli Arctic currents from northern regions; if so, the currents have conveyed tlie animal at an early 

 period of life to the new locality, where it has been able to subsist and develop further. The other 

 localit)-, in the Trondhjemfjord was previously recorded, and the Trondhjem Museum was in possession 

 of a defective specimen which was said to have been taken in the fjord ; but particulars were wanting 

 till the researches of the fjord in 191 1 brought to light, from the depth of 200 m., near Tantra, and 

 thus in the midst of the Atlantic water layers of the fjord, a well developed female polyp. This find 

 gives the more surprise, because there is left no opening for the possibility that the specimen .should 

 have been carried to this place from Arctic water layers. Like other Arctic hydroids, such as 

 Tubularia rcgalis Boeck, Coryi/iorp/ia grocnlandica (All man), and Stcgopoiiia plicatilr (G. O. Sars), 

 Myriofhcla phrygia thus thrives very well in the region of the Trondhjemfjord which is otherwise 

 characterized by Atlantic Lop/io/iclia-xeei^. This cannot, however, be turned to account as a proof 

 against the yVrctic character of the species; in the Trondhjemfjord all these species must be looked 

 on as Arctic relicts. 



Family Tubulariidae. 



"Hydroids forming colonies, or solitary, with large oviform or globose nematocysts in the ecto- 

 derm. The tentacles of the full-grown polyp are filiform and simply constructed with no central cavity; 

 they are arranged in two main circles, a proximal whorl round the broad basal portion of the polyp 

 and a distal whorl round the mouth. The basal whorl of tentacles is supported by a ring-shaped 

 mesogloeal cushion round the basal portion of the polyp. The ])olyi)s are radially symmetrical. The 

 supporting lamella shows a very simple structure". 



Most authors refer to this family also Braiichwcrriautlius, which I reckon as the type of a famih' 

 of its own, the Branchioccriautliidac. This family is distinguished from the Tiibulariidac partly b}- bilaterally 

 symmetrical polyps, parth- by the peculiar anatomical structure of the polyps. In fact, the structure of tlie 

 polyps of the Brancliioccriantliidac differs greatly from that of all other hydroids (comp. Stechow 1909). 

 There occurs a supporting lamella of complicated structure, and the polyp is provided with numerous, 

 prominent radial canals. They are distinguished from the Tnbnlariidar also in their inner anatomy by almost 

 lacking any trace of mesogloeal tissue at the base of the proximal whorl of tentacles, owing to the 

 radial canals. These points of difference are, indeed, of such importance that they fully justify the .sepa- 

 ration of Braucltioccriiiiillins into a family of its own, the Branchiocerianfliidac beside the Tubulariidae. 



Kuhn (191 3) divides the Tnbiilaiiidar into two subfamilies, Tubulariinac and Coryviorphinar. 

 The former he defines by the characters "KoloniebiUknd, IVriderm gut cntwickelt", while the latter 

 is defined as "vSolitiir, Periderm hautig oder riickgebildet, Wurzelhaare". To this is to be observed that 

 a species as Tubular in cornucopia Bonne vie is a typical Tubularia in sjMte of its forming no colonics. 

 The filamentary appendages of Coryviorplia must be compared with similar phenomena in JMyriothcla^ 

 some .species of which have rhizoid.s, while others such as Myrioflirla O^C/^j?' (Vi gurs), attach thems- 

 elves by a plateformed ])erisarc; when this is considered as nothing else or no more than a criterion 



