HYDROIDA 



51 



Material: 



Iceland: Talknafjoid (without particular data). 



Reydarfjord, depth 163 metres. 

 The Faroe Lslaiids (without particular data). 



Bougaiiivillia ('(vz/ivAHs a .southeru-boreal .specie.s penetrating as far as into the Mediterranean; 

 towards the north it goes, along the coast of Norway, only 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 \'et been pointed out at Greenland. As a new localit}' nnist be added the Faroe Island.s. The 

 species is indigenous to the litoral region. 



Gen. Perigonimus M- Sars. 



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

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

 still hydrocaulns, properly speaking, cannot be recorded. The polyps are fu.siform, with the tentacles 

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

 rounded b\- delicate pseudolndrothecae, 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 gonopliores are placed singly on the stolons or on 

 the ludranth stems, most frequently attached to the latter b}- a short stalk. 



The distinguisliing marks between Prrigoiiiiinis and Bongaiiivillia. indeed, seem to be so in- 

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

 Pcrigoiiiuius polyp, when wholly extended, is very easily mistaken for a Boiigaiiivillia. However, there 

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

 even belong to different families, the Boitgaii/7'illi(i-m&d\\sa.e being typical Margclida(\ while Prrigoiii- 

 iinis gives rise to Tinriifar (see Hartlaub 1913). As far as the nurse poly]) is concerned, we must 

 notice the difference existing between the wholly naked Boieg(//j/zu7/ia-\)o\yp and the hydranth covered 

 with pseudohydrotheca of the Prr/gfV//////ts-po\yp. The pseudohydrotheca has been pointed out by sev- 

 eral authors and has been emphasized as generic character particularly by Broch (1911). A closer 

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

 in the Adriatic species, Pcrigoiiiiinis Corii Hadzi and Perigonimus Gcorginae Hadzi; the latter .spe- 

 cies is very nearh- related to Perigoiii)inis rcpciis (Wright). Hadzi points out that Perigonimus 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. I-'or this jellied polyp case, which 

 is, in its outer margin, connected with the ectoderm (;f the polyp, I. therefore, emplo\- the denomina- 

 tion of "pseudohydrotheca", earlier emj)loyed for the chitinous false hydrothecae of Clafhrozoon. In the 

 case of Clilatlirozoon^ however, the formation seems to be quite different, and the denomination, on 

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



