34 



HYDROIDA II 



It is evidently this species which is partly mentioned under the term Lafoea pyg/// tea; according 

 to Hi neks (1868 p. 205) some of Alder's original drawings show a conical lid in this species, which 

 at once shows that Alder's specimens, or at any rate some of them, must have been Calycella syringa. 

 That Lafoea pygmaa is here only partly noted as synonymous with this species, is, as indicated under 

 Lafoea gracilli?/ia, owing to the fact that several writers at any rate have recorded creeping colonies 

 of the latter species under the same name. 



Calycella syringa appears to be a wholly cosmopolitan species, which has been met with in all 

 seas. Its bathymetrical area is very extensive, ranging from about 6 metres down to nearly 1500; it 

 should nevertheless be observed that its occurrence in the abyssal region is exceptional, its chief area 

 of distribution being restricted to the middle and upper parts of the littoral waters. Within the area 

 investigated (fig. X) we find that it is apparently lacking along the greater part of the east coast 

 of Greenland, where it is first met with far to the north, about 76 N. Its occurrence under high arctic 

 conditions is altogether scattered, save where an intermixture of warmer water is discernible. 



Gen. Tetrapoma Levinsen. 



Stolonial colonies with tubular or narrowly bell-shaped hydrothecse without diaphragm. Closing 

 apparatus formed by the original roof of the hydrotheca, and separated by a marked limitation from 

 the thicker hydrotheca wall; it consists of (four) separate triangular plates, each attached in a sinus, 

 between as many hydrotheca teeth. The polyps have a uniformly developed gastral endoderm, and 

 lack outer ectoderm lamellae. 



In a previous work (1909 p. 165) I united this genus with Lovenella. Kramp (1911 p. 383) 

 separates them again as two genera, chiefly, it would seem, on account of the number of plates in 

 the lid. This feature can hardly be called important as a generic character; there is, however, another 

 distinguishing feature of greater significance, which renders it necessary to separate the two genera. 

 Hincks (1868 p. 178) especially mentions in Lovenella clausa (Loven) the presence of a diaphragm, a 

 formation which does not appear to be found in Tetrapoma quadridentatum, and which warrants generic 

 distinction. Secondarily, this separation is supported by the fact that Tetrapoma has stolonial colonies, 

 while those of Lovenella are sympodial. 1 



Levinsen (1913 p. 283) observes in a footnote, regarding Tetrapoma, "This genus must, no 

 doubt, be united with Thyroscyphits". In this I am for several reasons unable to concur. In the first 

 place, Thyroscyphus has a distinct diaphragm, and hydrothecse of bilateral structure; in the second, 

 the structure of the polyp also is entirely different. Tttyroscyphus, with its ectoderm lamellae and inci- 

 pient blind sack formation, as also the differentiated gastral endoderm, exhibits closer relationship with 

 Scrhthtriidcr, and should probably far rather be considered as a primitive genus of this family. 



Tetrapoma quadridentatum (Hincks) Levinsen. 

 1874 Callycella qttadridentata, Hincks, On deep-water Hydroida from Iceland, p. 149, pi. 8, figs. 17 — 20. 

 1893 Tetrapoma quadridentatum, Levinsen, Meduser, Ctenophorer og Hydroider, p. 180. 

 1 Cump. also Lovenella corrugata Thornely (Broch 1914 p. 32). 



