I22 HYDROIDA II 



Unfortunately, the state of the material did not permit investigation of the structure of the polyp, 

 as to whether a blind sack has been developed or not; a query is therefore here appended to the 

 generic name. 



The geographical data for Abietinaria (f)fusea (fig. LXIV) present a somewhat scattered im- 

 pression of an atlantic species not penetrating far into the boreal waters. On the other hand, its 

 marked local restriction is highly surprising; the entire area of distribution of the species, or very 

 nearly so, is shown in the chart. Outside the areas marked, Abietinaria (f)fusca has hitherto been 

 recorded from the east coast of England and from Bohuslan (Sweden), as also, strangely enough, in a 

 single instance from the Kola Peninsula (Jaderholm 1909 p. 95). Once also — "Ingolf" St. 55 - 

 the species has been met with in the upper part of the abyssal region; otherwise, it has only been 

 taken in the lower part of the littoral. 



Gen. Sertularia (Linne). 



Upright colonies with embedded, bilateral hydrothecse, the opening with two large lateral teeth, 

 between which is a large abcauline and a smaller adcauline sinus; the latter may be divided into two 

 by a slightly prominent low median tooth. In each of the two main sinuses there is fastened a clos- 

 ing membrane, so that the closing apparatus consists of a smaller adcauline membrane without free 

 part, and a larger abcauline membrane with free distal part. The polyp has a well developed abcauline 

 blind sack. 



The organisation of the polyp warrants the distinction here made between Sertularia and 

 Dynamena. The genus Sertularia, as here laid down, forms a well-defined whole; the separation of 

 the different Sertularia species, however, is an extremely difficult matter, and it is important first of 

 all to take a survey of the various characters and their significance, in order to form an opinion as 

 to the value of the species described from northern waters. In Jaderholm's arrangement (1909 p. 

 25) we find under Thujaria the following Sertularia species: Sertularia Fabricii Levin sen, Sertularia 

 robusta Clark, Sertularia plumosa Clark, Sertularia vegae Thompson, Sertularia ar gen tea Linne, 

 Sertularia aipressina Linne, Sertularia inflata Schydlowsky, Sertularia Tolli (Jaderholm), Ser- 

 tularia Thompsoni Schydlowsky, Sertularia tenera G. O. Sars, Sertularia arctica A 11 man, and Sertu- 

 laria Birulm Schydlowsky; to this must be added the polyserial Sertularia mirabilis Verrill. There is no 

 doubt that the number of species must, on further investigation, be very considerably reduced. An 

 examination of the variations which may occur within a single large colony will suffice to convince 

 an unbiassed investigator that quite a number of the specific characters employed must be ranked 

 among the more or less accidental variations, while other characters again properly belong to the 

 category of developmental stages. It has not proved possible to procure indubitable specimens of all 

 the 13 species mentioned, but I am inclined to ascribe this in part to their lack of solidity. 



I have already in a previous work (1909 p. 171) pointed out that of the above-named species, 

 Sertularia arctica and Sertularia Thompsoni are undoubtedly synonymous with Sertularia tenera. Ja- 

 derholm's drawings (1909 pi. 9, figs. 7—9) clearly show that Sertularia vega- is synonymous with 

 Sertularia robusta, to which species Sertularia plumosa should also probably be referred. We have 



