Crustacea Malacostraca. II. 



By 



H. J. Hansen. 

 IV. The Order Tanaidacea. 



Introduction. 



Before entering on the subject of the present paper I may refer to the "Introductory Remarks" in 

 "Crustacea Malacostraca I" published in 1908, because they contain various statements that need not 

 to be repeated here. In that chapter I explained the limits of the area investigated by the "Ingolf" and 

 other Danish expeditions to our northern dependencies; the principal sources (apart from the "Ingolf") for the 

 material examined were enumerated and the principles followed as to "occurrence" and "distribution" 

 were laid down. Zoologists wishing to get some information on these and allied topics may find them 

 in the paper mentioned. 



Our earlier knowledge of the Tanaidacea inhabiting the seas around Greenland, Iceland and 

 the Fseroes was poor. Only 9 species were known, 2 of which belong to the family Apseudidae, 7 to 

 the Tanaidse. I am, however, inclined to think that no Carcinologist would have supposed that it 

 might be possible to discover more than ten or fifteen new species within that area. But in the 

 present paper I enumerate 78 species, all, excepting one, captured by Danish expeditions, and 52 of 

 these species are new to science. The "Ingolf has secured 71 of the species, but of these 13 have 

 besides been taken by another Danish expedition or by two or more zoologists; 3 species have been 

 gathered only by the "Thor" (Dr. Joh. Schmidt), 2 species exclusively by the second Amdrup-Expedition 

 (Mag. sc. Soren Jensen) and a single species by other zoologists. In proportion to the number of 

 species of Tanaidacea hitherto known from Norway, from Great Britain or from all seas together the 

 "Ingolf" collection is so astonishing, that some special reason may be looked for; it may be of 

 interest to attempt a discussion of the topic, and it may be possible to point out some results of 

 more general significance. Finally a treatment of some other results and questions may be inserted 

 before the purely systematic part. 



On the Literature. 9 



The earlier literature until the year 1881 comprises a good number of papers, but most among 

 them dealing with only a single form or with some few species; the largest and most valuable of 

 these contributions were written by H. Kroyer (1842) and W. Lilljeborg (1865). But in 1881 G. O. Sars 

 published his paper : Revision af Gruppen : Isopoda chriifcra (Arch. Math, og Naturv. Bd. 7), which is 

 epoch-making in the history of our order. He divided it - he named it a group - - into two \vell- 



The Ingolf.Kxpedition. lit. }. 



