104 HYDRO1DA II 



Sertularella Gayi is an atlantic warm-water species, which in the northern waters (fig. LV) exhibits 

 an easterly distribution. It belongs to the deeper littoral and upper abyssal regions, where it is parti- 

 cularly frequent. In the south-eastern part of the boreal area it is quite common, and moves hence 

 down into the cold area in the Faroe Channel; it is not altogether rare off the south coast of Iceland, 

 where it seems now and again to have been confused with Sertularella polyzonias. The "Ingolf" has 

 a single specimen from St. 94, so that the species can also occur in deep water off the south-east 

 coast of Greenland, outside the mouth of Danmark Strait, where the deeper parts are still covered 

 with warmer atlantic water layers. 



Sertularella tenella (Alder) Hincks. 



1856 Sertularia tenella, Alder, A notice of some new genera and species, p. 357, pi. 13, figs. 3 6. 

 1868 Sertularella tenella, Hincks, A History of the British Hydroid Zoophytes, p. 242, pi. 47, fig. 3. 



Upright, unbranched or slightly branched openly constructed colonies with monosiphonic hydro- 

 caulus. Stem and branches are divided by joints into not very long internodia, each having on 

 its distal part a very slightly imbedded hydrotheca; proximally, the internodium is furnished with a 

 pair of rings. The stem and branches are bent to an angle at the nodes, which gives them a mark- 

 edly zigzag course. The hydrothecae are large, about as long as the internodia, elongated oval, 

 with somewhat more cylindrical opening part; they are distinctly furrowed transversely between the 

 base and the cylindrical opening part. The aperture is set perpendicular to the longitudinal axis of 

 the hydrotheca. The opening margin has four low teeth, and in the sinuses between them four tri- 

 angular lid plates. The polyp has a well-developed abcauline blind sack. 



The gonothecse proceed from stem and branches close under the base of the hydrothecae. They 

 are oval to more pear-shaped, transversely furrowed throughout their entire length, and furnished with 

 a distal central short, almost cylindrical neck. 



Material : 



.1: 



"Ingolf St. 94 6456' N., 36i9' W., depth 204 fathoms 4,1 

 - 95 6 5 0l 4' N -> 339' W., 752 2,i c 



As a synonym to this species I have previously (1909 p. 126) noted Sertularella pellucida. Ja- 

 derholm has, however, (1909 p. 99, Taf. XI, figs. 8 n) given a closer study of this species, from 

 which it appears that it does not belong here, its entire structure being different, and the colonies 

 more resembling those of Sertularella fusif or mis. 



Kramp (1914 p. 1037) characterises Sertularella tenella as a cosmopolitan species. This must, 

 however, as will be seen from the chart (fig. LVI) be taken with some little reserve. The species is alto- 

 gether more sporadic in its occurrence within the northern waters, save probably for the tracts immediately 

 round the British Isles, where it appears to be more common. Otherwise, it follows in the northern areas the 

 same laws as do the warmer atlantic species, and is somewhat rare in the strictly boreal water layers, 

 v. Lorenz, (1886) mentions the species from Jan Mayen, but this determination would seem, from the 

 remaining data, to be somewhat uncertain. 



