CRUSTACEA MALACOSTRACA. 



Under <: occurrence are given the discoveries within the region definitely defined above for 

 the purpose of this investigation; under <: distribution the localities outside this region. Both and 

 especialh- the distribution have caused the author considerable practical difficulties and some remarks 

 on this subject will for several reasons be of service. All the ;Ingolf • localities are mentioned under 

 each species. On the other hand, it would take up far too much space to give all the localities for 

 a number of common species living in shallow water, especially for a no small number of Decapoda; 

 in such cases I have contented myself with summaries for each main section of the coasts. In many 

 cases, however, it is a matter of opinion how much might be usefully included and the correctness of the 

 view adopted may indeed always be combated; some will undoubtedly think that I give too many 

 details, others perhajjs that I give too few. While it is difficult enough sometimes to find a suitable 

 mean with regard to how many details based on our own investigations should be given, it becomes 

 still more difficult to determine how much should be noted of the data of other authors concerning 

 the occurrence of an\- species within the region mentioned. Sometimes the inclusion of such data is 

 superfluous as I myself have seen the species from the same and quite adjacent localities, yet the 

 exclusion of a citation may sometimes be considered as due to lack of knowledge or a slight. In 

 other cases these older data are of doubtful quality — sometimes even the supposed data prove 

 incorrect when the author's specimens are examined — so that the question of their inclu.siou or 

 omission becomes even more difficult. If I were to indicate all the earlier notices and in every little 

 case of doubt give a criticism, I should certainly succeed in securing myself against the complaint 

 mentioned, but it is very doubtful whether I should advance science by being so unnecessarily prolix. 

 What I include of the literature therefore depends upon personal opinion, but I have endeavoured to 

 give a correct and complete picture for each species. 



The distribution both geographical and bathymetric is given for each species. We often meet 

 with a kind of list of the distribution of each species in the literature, but such a list's contents are 

 too often defective, inexact or uncritical. It is defective when the author has passed over older and 

 probably correct data of localities of real interest, it is inexact when the author for example mentions 

 Greenland without distinguishing whether a form is known from one of the two so diverse seas as 

 those at West Greenland and North-East Greenland (from the more southerly East Greenland only a 

 little is known from Angmagsalik). And it is not rarely tangibly uncritical, which is the worst, when 

 one finds in a list statements of occurrence or distribution which depend upon incorrect determinations 

 on the part of the author or his predecessors. In the Decapoda, Mysidacea and two other smaller orders 

 there is fortunately slight possibility of difficulties of this kind, but it is very common in the Tana- 

 idacea for example and especially the Amphipoda. These shortcomings have obliged me, especially 

 for the Decapoda, to undertake a work which I found very great, possibly greater than the matter 

 was worth from the present standpoint of our knowledge, in order to give a somewhat complete and 

 at the same time as far as possible critical report on the geographical distribution of mam' species 

 — so far as this is known at present. But it has to be added, that there are very few species of which 

 it may be said that our knowledge is complete, the boundaries either in America, or north of Asia, or 

 in the south of Europe or west of Africa being very imperfectly known. It is also the case, at least 

 for a number of species, that the depth at which a given form occurs in one sea is much less than 



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