STYLASTERIDAK 19 



confirmed the correctness of Sars' supposition. — Since Storm (1882 p. 169) some years later mentioned 

 the occurrence of the species in the Trondhjem Fjord, we find little or nothing in the literature regarding 

 its occurrence on the west coast of Norway. 



The species has been figured however by P. M. Duncan 11874 PI. 49 figs. 1—3) from material 

 from the Porcupine:; the identity of the colony from the figures given cannot be doubted, though 

 the author refers it erroneously to Stylaster gemmascens. Moseley (1881 p. 85) notes the species under 

 the name of Allopora oculina; Hickson (1888 p. 594) mentions the species from the Hardanger Fjord 

 as Allopora oculina and from the Tritons Expedition as Allopora norvegica. Apart from the doubt 

 whether the two species belong together, the present species must in any case under the international 

 rules of nomenclature retain the specific name which was given it already by Gun n er us in the year 1768. 



Remarks on the affinities and systematic position 



of the Hydrocorallines. 



After L. Agassiz in 1859 had pointed out the Hydroid nature of the Millepora and Moseley 

 in 1878 had indicated, that the organisation of the Stylasterids also characterised them as Hydrozoa, 

 no one has doubted that the Hydrocorallines are most nearly related to the Hydroids and in reality 

 must be regarded as highly specialised Hydroids, whose main characters are the power of the colony 

 to form a skeleton of calcium carbonate and the polymorphic development of their polyps. 

 These are thus the main characters which mark off Moseley's order Hydrocorallinac. 



Closer consideration of these characters entitles us to doubt, however, whether on such a basis 

 we are justified in raising the Hydrocorallines to the rank of a special order. If we compare them 

 for example with the large order of corals, we see how the greater or less ability of the colonies to 

 separate out carbonate of lime — as for example in the Umbellula species — is only regarded as a specific 

 character and is not even sufficient for a generic separation of the species, unless the lime-excreting function 

 is combined with distinct morphological changes in the individuals or colonies. It is thus a question, whether 

 the latter is the case or not when we compare the Hydrocorallines with the Hydroids. We must therefore in 

 the first place endeavour to ascertain, to which of the Hydroids the Hydrocorallines are most closely related. 



The first hint is obtained from the tectonic structure of the colony itself. The fine anastomosing 

 canals of the decalcified Hydrocoralline are quite homologous with the stolons of the Hydroid colony; 

 we thus remark a conspicuous resemblance between the Stylasteridac and the Hydroceratinidae '). 

 Even the structure of the colony agrees exactly in Clathrozoon Wilsoui Spencer and the primitive 

 Stylasteridae, only the chitin of the skeleton being replaced in the Stylasteridac by a thick layer of 

 calcium carbonate. Another Hydroid group also, Solanderiinae (family of Cory//idae, cf. Kiihn 1913) 

 shows the same structure of the colony and can be imagined as standing near the parent stem of the 

 Hydrocorallines. 



The structure of the polyp will perhaps show the further line of connection. Most Hydroid 

 investigators lay great stress systematically on the form of the tentacles and consider them one of the 

 principal phylogenetic characters. Moseley (1881 p. 46) maintains, that the tentacles of the Hydro- 



■) By Kiihn (1913 p. 22S) the Hydroceratinidac are considered a subfamily of Bougainvilliidae. 



