■ 2 HYDROIDA 



added the^seas to the south of the Faroe Islands at the depth of 70—150 fathoms. All the finds are 

 thus situated in the boreal area, on the border of the warmer Atlantic regions (Text-fig. L). 



Gen. Monobrachium Mereschkowsky. 



Reptant colonies, whose cylindric polj'ps are provided with a solitary large tentacle. Besides 

 the nourishing individuals bearing tentacles, also machozooids with no mouth and no tentacles occur. 

 The polyps have no distinct stem and are not covered with perisarc. The gonophores are eumedusoid 

 and attached to the stolons. 



The very peculiar Arctic genus of hydroids first described by Mereschkowsky (1877) has been 

 more closely investigated by Wagner (1890) and Bonnevie (1899). In the only species known of this 

 genus the eumedusoid gonophores have a rudimentary spadix, and the germ cells are accordingly 

 developed along the radials canals. On this ground Bonnevie maintains that the species is closely 

 related to the Leptomcdiisae, and tliat the genus has to be placed proximately between athecate and 

 thecaphore hydroid.s. Kiihn (1913), on the other hand, holds that the organisation of the gouophore 

 cannot be considered as any certain proof justifying such a supposition, and points out that the trans- 

 ition of the gouophore from independent free existence into sessile mode of life can effect a secondary 

 displacement of the gonads in many different ways without any necessity that this should be indica- 

 tive of nearer or remoter relationship. Apart from this, however, there is au additional reason against 

 the supposition of Bonnevie. As is pointed out by Vanhoffen (1909), we have in hand a medusa- 

 form obviously nearly related, Catablrina, which, when somewhat damaged, is very easily mistaken 

 for a Lcptomedusa^ but which i.s, in fact, a genuine Tiaridc. Vanhoffen even presumes that Cata- 

 blfiiia really is the medusoid generation of MoiiobyacJiiitvi. But in that case it remains to show that 

 the gonopliores of Moiiobrac/iiiiiii are not sessile as they have hitherto generally been supposed to l)e. 



The explanations of Vanhoffen (1909) and Kiihn (1913) make good \.\\a.i Moiiobrac/iiiiui takes 

 no intermediate place between athecate and thecaphore hydroids. But the place of the genus among 

 the athecate ludroids would still be equally uncertain if tlie peculiar species Campaniclava clionis 

 Vaulioffen (1909) had not shown us, by its heterogeneous development of the tentacles, the unquesti- 

 onable link between Monobrachium and the normal-looking forms of Clava. Therefore there is no 

 reason an)- longer to regard the genus as the representative of a jjeculiar family; as pointed out by 

 Vanhoffen, it ought to be cla.ssed with the Clavidae. 



Monobrachium parasitum Mereschkowsky. 

 1877 MoHobrac/iiniii pnrasifiiiii, Mereschkowsky, On a new Genus of Hydroids, p. 225, pi. 5 fig. 1—6 



pi. 6 fig. 7—14. 

 1899 — parasiticuiii Bonnevie, Norske Nordliavs Expedition, p. 51. 



Reptant colonies, whose polyps are dimorphically developed; beside cylindric polyps with ori- 

 fice and a vigorous tentacle, also machozooids without mouth or tentacles occur. The nourishing 



