424 b'AR TrÄGARDH. 



Remarks 



on the composition of the acarid fauna of the region 



explored by the Danmark Expedition. 



In all 7 species were discovered by Mr. Johansen, which are 

 distributed amongst the different families as follows: Parasitidœ 2, 

 Trombidiidœ 2, Hydrachnidœ 1, Oribatidœ 1, Sarcoptidœ 1. 



It is obvious that this collection is not exhaustive, and that 

 further investigations will reveal several more species. Especially 

 the Oribatidœ are undoubtedly far better represented than the present 

 collection seems to indicate. As is well known the main part of 

 the species belonging to this group are fungivorous or lichenivorous; 

 as a consequence, they are able to find shelter and means of sub- 

 sistence wherever lichens and fungi are to be found, whereas the 

 carnivorous Parasitidœ and Trombidiinœ are dependent on the occur- 

 rence of other small arthropods, partly Collembola and Thysanura, 

 partly other mites as well as larvæ of insects. 



The fundamental difference as regards the food of the groups 

 greatly influences their geographical distribution. 



In a paper on the Acari of Sarek-tjåkko (1911) the author in- 

 vestigated amongst other things this problem and proved that, while 

 of the Oribatidœ 42.1 ^Vo ascended to the regio alpina superior, only 

 17 *^/o of the Parasitidœ went as high. 



If we compare the actual number of both groups the difference 

 between them becomes still more evident, only 4 Parasitidœ being 

 recorded from the regio alpina superior against 16 species of Ori- 

 batidœ. 



There is no reason why the numerical proportion of these two 

 groups should not be about the same in East-Greenland as in the 

 above mentioned part of Sarek-tjåkko, and consequently we are, in 

 my opinion, justified in assuming its fauna to be considerably richer 

 in Oribatidœ ; the same also probably applies in some degree to the 

 Trombidiidœ. 



All the terrestial mites now recorded are widelj' distributed 

 forms which occur in many parts of the arctic region, and some of 

 which are also to be found in the palæarctic region. 



Three of them, Eulœlaps ambulans, Parasitus fucorum and Tyro- 

 glyphus fucorum doubtless owe their wide distribution to their bio- 

 logical relations to other animals, the lemming and the humble-bees 

 and it is of great interest to notice that the two former are the only 

 Parasitidœ yet found on the East-coast of Greenland. 



