IIVDROIDA II 187 



The explanation of the distribution in these two families must therefore be sought in the 

 current conditions, and we here obtain a very good idea in the case of Aglaophcniidir. The currents 

 in Davis Strait have as yet been only very little investigated, but we know that there is an atlantic 

 current moving up from the deep towards Store Hellefiskebanke and thus depositing larvae in the 

 cul de sac before mentioned. In the case of the Norwegian Sea, the currents are better known. On 

 glancing at the chart (fig. XCV) and comparing it with the occurrence of Aglaopheniidtz, the solution 

 is at once apparent An atlantic current runs northward in the eastern part of Danmark Strait and 

 sends a branch thence along the north side of Iceland and then southward along the east coast; this 

 branch will thus carry larvae from Danmark Strait and deposit them here and there along the coastal 

 banks north and east of the island, where some few of them are able to develope further. This at 

 once explains the scattered occurrence of Aglaopheniida in these waters. The main force of the 

 northgoing atlantic current, however, is concentrated in the Faroe Channel, and here carries 

 the larvae in over the Wyville-Thomson ridge. Along the north side of this ridge, then, we find the 

 heaviest ''rain" of exotic larvae in the Norwegian Sea, and here also the greatest percentage of indi- 

 viduals probably capable of developing further, provided they can stand the immersion in the icy 

 waters of the cold area at all. A branch of the same current runs southward along the east coast of 

 Scotland and England, causing a scattered occurrence of Aglaopheniidce . able to develope in shallower 

 water, such as species belonging to the genera Aglaophenia and Thecocarpus. Other larvae drift farther 

 on with the main current, and sink to the bottom on the Norwegian coast plateaus, or the edges of 

 the same, or are occasionally carried as far up as Spitzbergen, whence several finds of Aglaopheniidce 

 have been recorded, where offshoots from the Atlantic current break in over the plateaus in the shal- 

 lower Murmau Sea. 



It would be of no value here to group the species investigated according to the separate geo- 

 graphical categories. Such arrangement has been made several times in recent works by Kramp 

 (1914) and myself (1909 and later works). It should merely be pointed out that purely boreal hydroids 

 are extremely rare, if indeed we can, after exhaustive investigation, maintain any such at all. 



We may now proceed to a closer comparison of the hydroid fauna as it appears in the areas 

 represented by Greenland, Iceland and the Faroe Islands. With regard to the two first-mentioned 

 areas, surveys have recently been published by Kramp (1914), and Saemundsson (1911); the latter, 

 however calls for certain corrections, and there are also some few additions to be made. 



Of the species here dealt with, the following have been met with in West Greenland waters 

 (species new to the area are indicated by a *). 



*Coryne Loveni Monobrachium parasitum Eudendrium annulatum 



Myriothela phrygia *Hydractinia Sarsii capillare 



Tubularia indivtsa echinata Lafaa dumosa 1 



Corymorpha groenlandica *Perigonimus abyssi 



*Branchiocerianthus reniformis roseus gracillima 



IClava multicornis Eudendrium rameum Toichopoma obliquntn 

 i In the previous chapters the name has erroneously been spelt Lafofa. 



24* 



