On Norwegian Hydroida from Deep Water. 125 



XVIII, — Notes on Norwegian Hydroida from Deep Water. 

 By the Rev. Thomas Hincks, B.A., F.R.S. 



A PAPER of remarkable interest has just been published by 

 G. Ossian Sars on the deep-water Hydroida of the Norwegian 

 seas *. The investigations of this excellent observer, who 

 worthily carries on the work of his distinguished father, have 

 established the fact that a very varied Hych'oid fauna exists 

 in this region at depths varying from 50 fathoms to 300 

 fathoms. It comprises no less than fifty-eight species, of 

 which sixteen appear to be new to science. From the tables 

 (showing the distribution of the Norwegian Hydroids both 

 vertically and horizontally) which are appended to the descrip- 

 tive portion of the paper it appears that the most productive 

 region lies between 50 and 100 fathoms. In this zone about 

 two thirds of the whole number of species recorded for Norway 

 have occurred (fifty -four out of eighty-four). 



The littoral region, as might be expected, is barren, yielding 

 only six forms — a striking contrast to the corresponding zone 

 on our own shores, which teems with Hydroid life. The 

 Laminarian is hardly more fruitful, giving eleven, of which 

 two are common to it and the preceding. From 10 to 20 

 fathoms thirteen species have been obtained, from 20 to 50 

 (the "Coralline region") forty-two. Below 100 fathoms the 

 numbers diminish with the increase of depth ; from 300 fathoms 

 only five species have been procured [Plumularia gracillima^ 

 n. sp., Filellum serpens j Lafoeina tenuis ^ Gampanidaria ver- 

 ticillata^ and Perigonirtms abyssi, n. sp.). The last of these 

 alone passes the 300-fathora limit, and actually reaches 400. 



If we except the fragments of a supposed Hydroid, brought 

 up by the dredge of the 'Porcupine ' from a depth of 2435 

 fathoms, of which nothing definite is known, the extreme 

 vertical limit of Hydroid distribution would seem to lie between 

 600 and 700 fathoms, so far as our present hnowledge goes. 

 And it must be remarked that below three hundred fathoms 

 a very small number only of forms have been obtained, a few 

 straggling outliers, several of which seem to be much more at 

 home in more moderate depths. In no sense can the Hydroida 

 be considered an abyssal tribe. 



In the chapter on " Distribution in Space " in Allman's 

 ' Monograph of the Tubularian Hydroids ' he places the maxi- 

 mum of development in tlie Coralline zone ; but on the Nor- 

 wegian coast it must be assigned to the " deep-water region " 

 immediately succeeding it, which yields fifty-four species 



* Bidrag til Kundskaben om Norges Hydroider. Af G. O. Sars. 

 Med 4 autographiske Plancher. 1873. 



Ann. & Mag. N. Hist. Ser. 4, Vol.xVn. 10 



