Desuden bai- jeg i de sidst forlobne Somre under 

 Ophold ved Krlstianiafjorden, paa forskjellige Steder ;ii' 

 Vestlandet, i Lofoten og ved Trondhjemsfjorden liavt Anled- 

 ning til selv at studere Hydroidefaunaen paa levende Indi- 

 vider, og at iagttage de i Planktonet levende Meduser. 



For at faa iudordnet Nordbavsexpeditionens Hydroider 

 paa sine Pladse i det System, der efter mine UndcrsGgelser 

 staar for mig som det naturlige, har jeg for hver Slægt 

 opstillet et Scbenia. der omfatter disse, sammenstillet med 

 Xorges Hydroider. der dels er kjendte fra for af som nor- 

 ske, dels nye for vor Fauna og dels er de ikke tidligere 

 beskrevne. ^ 



Bemerkninger om den senere Tids Literatur. og 

 om Grundlaget for et naturligt System. 



H'nii:],ti og Alhiiaii har i sine klassiske Verker — (57) 

 1868 og (14) 1872. — givet en en Oversigt over den ældre 

 Hydroideliteratur. og sat dens Resultater i System, hvorved 

 de i hoi Grad har lettet Arbeidet for de senere Forskere. 



Men efter denne Tid er Kjendskabet til Hydroiderne 

 blevet sterkt udvidet. idet der er udkommet en stor Mængde 

 Afhandlinger med Beskrivelser af nye Slægter og Arter 

 fra de forskjellige Steder. Ofte luangler enhver Angivelse 

 af det System, hvorunder Forfatteren tænker sig Arterne 

 indordnede. — Alhiioii bar selv (19) forladt sit tidligere 

 System og oprettot et nyt, der er i hoi Grad unaturligt, 

 Hgesom han har oprettet en Række nye Slægter, hvoraf de 

 fleste er haseret kun paa Artskarakterer — og Hydroidernes 

 Systematik var saaledes bleven sterkt kompliceret, paa 

 samme Tid som Literaturen, bestaaende af talrige spredte 

 Afhandlinger. var meget vanskelig at overskue. En Revi- 

 siou var derfor hoist paakrævet, og i de sidste Aar er der 

 da ogsaa gjort kraftige Ski'idt i Retning af en Forenkling 

 af Systemet. 



Levinsen (79) gjorde i 1893 Begyndelsen. idet ban. 

 foruden at give meget interessante Meddelelser angaaende 

 enkelte Punkter af af Hydroidernes Anatomi, ogsaa sam- 

 menfattede en Del ældre Familier under Fam. Bougain- 

 rilJidæ. og forovrigt gav temmelig omfattende Diagnoser af 

 flere andre Familier. Han hævder, at man under Slægts- 

 inddelingen ikke kan tåge Hensyn til, hvorvidt Gunoforerne 

 udvikler sig til iVi Meduser eller ikke, og dette gjennera- 

 forer han i Systemet paa en enkelt Undtagelse nær 

 (nemlig hvor han retter sig efter den almindelige Praksis, 

 og føreslåa r '!^A\\\eti Halisiplionia for saadanne Lafoea-Arter, 

 der frembringer Meduser). Men paa samme Tid som ban 

 saaledes indleder en Forenkling af Systemet, saa opretter 

 ban selv under Camjintiiilinhlæ en Række nye Slægter, der 

 elter min Opfatning ikke bar Existensberettigelse som saa- 

 danne; de er nemlig grundede paa Kjendemerker, der er 

 meget gode for Artsbestemmelsen, men som dog neppe kan 



I have, moreover, during the last few summeis on the 

 Kristiania Fjord, in various places on the west coast, in 

 Lofoten and on the Trondhjem Fjord, had occasion of stu- 

 dying the hydroid fauna from living specimens, and of 

 ohserving the medusæ living in the plankton. 



In order to give the hydroids of the North Atlantic 

 Expedition their proper place in the system which after 

 my investigations, seems to me, to be the natural one, 1 

 have drawn up a tahle for each genus, in which they are 

 placed side by side with Norwegian hydroids. some of them 

 being already known as Norwegian, some new to our fauna, 

 and some not previously described.' , 



Remarks on tlie literature of regent times, and on the 

 foundation for a natural system. 



Hind:» and AlJnian, in their works — (57) 1 8G8 and 

 (14) 1872 — have given a general view of the earlier hyd- 

 roid literature, and systematised its results, thereby greatly 

 lightening the labour of suhseipient investigators. 



But since that time, the knowledge concerning liydroids 

 bas been greatly extended, a great number of treatises 

 having appeared with descriptions of new genera and spe- 

 cies from the most varied localities. Frequently all meu- 

 tion of the system according to wiiicb the author places 

 the species is wanting — Alhnan himsclf (19l abandoned his 

 previous system, and set up a new one which is extremely 

 unnatural; and he has also established a series of new 

 genera, the greater nnmber of which are based only upon 

 speciflc characters — and the systematisation of the Hyd- 

 roida iiad thus become highly complicated, while at the 

 sanu' time the literature, consisting of numerous scattered 

 treatises, was very difficult to survey. A revision was thus 

 extremely ueedful, and of late years decided steps have 

 been tåken in the direction of a simplification of tlie system. 



Levinsen (79) made a commencemeut in 1893, when, 

 besides imparting very interesting information concerning 

 certain points in the anatomy of hydroids, he collected a 

 number of older families under the family BongainviUidæ, 

 and also gave fairly comi)rehensive definitions of several 

 other families. He maintains that in dividing into genera, 

 no regard can be paid to the question wbether the gono- 

 phores develope into medusa or not, and he carries tbis 

 out in his system (with one exception, viz. where he eon- 

 forms to the general practice, and proposes the name 

 Halisiphonia for such species of Lajoea as produce medusæ). 

 But while thus introducing a simplification of the system, 

 he himself estabUshes, under Cainiianidinidæ. a series of 

 new genera, Avhose existence as such is. in my ojjinion, 

 without justification. for they are founded on distinguishiug 

 features which are good enough for determining species, 

 but which can scarcely have tbc importance which Levinsen 



En Beskrivelse af disse uye norske Arter fremkommer i Bergens 

 Mnseuuis Aarbog for 1S08 i eu Afhandling, der sendes i Tryk- 

 ken samtidig med denne. 



' A description of these new Norwegian species will appear in the 

 Year-book of the Bergen Museum for 1898, in a paper which 

 goes to press at the same time as the present one. 



