HYDROIDA ci 



Material: 



Iceland: Talknafjord (without particular data). 



Reydarfjord, depth 163 metres. 

 The Faroe Islands (without particular data). 



Boitgaiiivillia cw^/cr/rf is a southern-boreal species penetrating as far as into the JMedilerranean; 

 towards the north it goes, along the coast of Norway, onl\- as far as Lofoten. It has been recorded several 

 times from Iceland, in the warmer water-layers along the west- and south-coasts of the island, but it 

 has not yet been pointed out at Greenland. As a new locality must be added the Faroe Islands. The 

 species is indigenous to the literal region. 



Gen. Perigonimus M Sms. 



The hydranth stems rise immediately from the reptant stolons, or there are formed upright 

 rhizocaulomes bearing the polyps. The polyp stems are sometimes divided into a coujde of branches; 

 still hydrocaidus, projierly speaking, cannot be recorded. The polyps are fusiform, with the tentacles 

 placed in a whorl below the conically pointed oral portion; below the tentacle whorl they are sur- 

 rounded by delicate pseudohydrothecae, superiorly connected with the ectoderm of the hydranth, and 

 inferiorly passing into the chitinous perisarc of the stem. The stinging cells show attempts at being 

 arranged in transverse belts on the tentacles. The gonophores are placed singh- on the stolons or on 

 the hydranth stems, most frecpiently attached to the latter by a short stalk. 



The distinguishing marks between Prrigoiiimiis and Boitgaiiivillia. indeed, seem to be so in- 

 significant that the conclusion might be obvious that both genera should be united into one. The 

 Perigouiiniis polyp, when wholly extended, is very easily mistaken for a Bougainvillia. However, there 

 is an essential difference between the two genera which necessitates a separation. Their medusae 

 even belong to different families, the Bougaiuvillia-\\\^(\\\s7K^ being typical Margelidai\ while Pcrigoni- 

 III us gives rise to Tiaridac (see Hartlaub 1913). As far as the nurse polyp is concerned, we must 

 notice the difference existing between the wholly naked Bougaiiivillia--^o\\\< and the hydranth covered 

 with pseudohydrotheca of the Pcrigoiiiiiiiis-\io\\i^. The pseudohydrotheca has been pointed out by sev- 

 eral authors and has been emphasized as generic character particularly by Broch (ign). A closer 

 inquiry into this formation has been made by Hadzi(i9i3, 1914), who has studied it most thoroughly 

 in the Adriatic species, Perigoiiiiiius Corii Hadzi and Pcrigoiiiiiiiis Georginac Hadzi; the latter spe- 

 cies is very nearly related to Perigoniiiiits rcpciis (Wright). Hadzi points out that Berigonivtns is 

 provided with a sort of hydrotheca, the essential substance of which is jellied and accordingly not 

 entirely parallel with the hydrotheca of the thecaphore hydroids. For this jellied polyp case, which 

 is, in its outer margin, connected with the ectoderm of the polyp, I, therefore, employ the denomina- 

 tion of "pseudohydrotheca", earlier employed for the chitinous false hydrothecae of Clathrozoon. In the 

 case of Chlalhrosoon, however, the formation seems to be quite different, and the denomination, ou 

 that account, rather misleading; indeed, we had better employ the term of "false hydrothecae". Hadzi 



