Geographical distribution of the Echinoidea of the 



Northern Atlantic. 



The revision of the Echinoidea of the Northern Atlantic given in this work leads to some 

 zoogeographical results which differ not inconsiderably from those laid down in the careful and 

 extensive studies on the geographical distribution of Echinoidea in the works of Professor Agassiz, 

 the differences mainly resulting from the many corrections in the interpretation of the species and 

 genera of Echinoids, not from a disagreement in the principles and general treatment of the zoogeo- 

 graphy of this group of animals. In fact, I quite agree with Ortmanu (Grundziige der marinen Tier- 

 geographie. 1896) in regarding Professor Agassiz' zoogeographical work on the Echinoids as den 

 Gipfelpunkt der bisherigen tiergeographischen Forschung, wenigstens atif dem Gebiete des marinen 

 Literals (p. 6). Quite recently Professor Doderlein has treated the distribution of the arctic and 

 subarctic Echinoidea (Arktische Seeigel. Fauna Arctica. IV. 2. 1905) very carefully, but in a way which 

 differs considerably, and, as it seems to me, not fortunately, from that in which Agassiz treats the 

 matter. My views thereof are far more in accordance with those of Professor Agassiz. 



The study of the geographical distribution of the Atlantic species of Echini leads us to recognize 

 the following regions or districts: The Arctic littoral and abyssal, the European boreal, the Me- 

 diterranean, the West African tropical littoral and the East American littoral; further three 

 Atlantic Deep-Sea regions: the European, West African and East American. Each of these 

 regions is characterised by some species peculiar to it and by the absence of a number of species 

 occurring in the adjoining regions. 



What limits these different regions is not the latitude and longitude, but the physical conditions 

 of the sea, above all the temperature. To take the Polar circle or a line from the North Point of 

 New Foundland to the point of the Norwegian Coast which lies on the Polar circle as the limit of 

 the arctic or subarctic region, as is done in Doderlein's work, is arbitrary; it will scarcely be pos- 

 sible to produce scientific reasons for this limitation of the regions, which leads to such results as 

 to count e. g. Phormosoma placenta to the Arctic Fauna. Just as the marine fauna of the Ber- 

 mudas really belongs to the tropical West Indian Fauna, though the islands are situated on 32 L,at. N., 

 the Gulf Stream making the physical conditions suitable for tropical animals, in the same way the 

 fauna of the warm area of the Atlantic proceeds far towards the North, and conversely, the arctic fauna 

 far South, if the conditions are only suitable. Along the European side of the Atlantic the Gulf 

 Stream, as is well known, proceeds along the Coast of Norway even to the White Sea and produces 

 such physical conditions as to enable forms of the warm area to proceed to the North Cape, 71 L,at. N., 

 whereas on the American side the cold Labrador Stream passes far towards the South, enabling the 



The Ingnlf-Expedition. IV. 3. 23 



