182 ECH1NOIDEA. II. 



almost cosmopolitan, the statements are, as far as I have been able to ascertain, all founded on wrong 

 determinations. (Of Echinocardium flavescens I have not myself seen American specimens, but the 

 descriptions point towards the American form representing a distinct species ; comp. above p. 136). 



One species, Spatangus Raschi, is common to the boreal and the European and West African 

 Atlantic regions. The following species have a wide distribution in the whole of the Northern At- 

 lantic : Dorocidaris papillata, Echinus Alcxandri, elcgans, Brisaster fragilis and Hcmiaster expergitus. 

 Two of these species have as yet only been found a single time in the boreal region, viz. Echinus 

 Alexandri and Hemiaster expergitus, and are perhaps only occasional visitors there. Dorocidaris pa- 

 pillata, Echinus elcgans and Brisaster fragilis are widely distributed on the Norwegian plateau, but 

 they must evidently be regarded as intruders from the Atlantic region, which may perhaps also hold 

 good for Spatangus Raschi. To suppose that they should have originated in the comparatively small 

 area along the Norwegian Coast and from there have spread over most of the Northern Atlantic 

 (Dorocidaris papillata also to the Mediterranean) would not seem very reasonable, whereas on sup- 

 posing their home to be the Atlantic region their extension over the Norwegian Coast-Plateau becomes 

 easily intelligible on account of the considerable influence of the Gulf Stream there. One of them at 

 least, Dorocidaris papillata, has pelagic larvae, which must facilitate the spreading over wide areas. 



One of the species occurring in the boreal region, Strongyloccntrotus drolachiensis, is beyond 

 doubt an intruder from the Arctic littoral region. In the same way Paraccntrotus lividus and Sphcer- 

 echinus granularis, which occur in the southernmost part of the regions are intruders from the Medi- 

 terranean and West African regions. 



On the American side there is no region corresponding to the European boreal region. The 

 Arctic region here proceeds so far southwards and the tropical region so far northwards that there is 

 no room for another region. The short tract from Cape Cod to Cape Hatteras forms an intermediate 

 zone, where the faunas of the two regions meet and intermingle, corresponding to the Lusitanian dis- 

 trict on the European side of the Atlantic. 



The Mediterranean region comprises, besides the whole Mediterranean Sea, the littoral zone 

 of West Africa down to about Cape Bojador, the Canaries, Madeira and the Azores. On account of 

 our very insufficient knowledge of the littoral fauna of West Africa it is for the present impossible to 

 give the southern limit of this region more exactly. Perhaps it ought really to go down to Cape 

 Verde; it seems, however, more probable that the tract from Cape Verde towards Cape Bojador will 

 prove to be the intermediate zone between this and the West African tropical region. 



It may be concluded from the fact that the connection between the Mediterranean and the 

 Atlantic through the Gibraltar Strait is of comparatively very recent origin, that several forms of its 

 present fauna of Echinoids have immigrated from the Atlantic. In accordance with this is the fact 

 that no true deep-sea Echinoids are found in the Mediterranean; they have not been able to pass 

 the Gibraltar Strait, where the greatest depth is only about 300 M., as is also the case with the cold 

 water from the deeper layers of the Atlantic, the bottom temperature in the Mediterranean being 13 

 even to the greatest depths, more than 4000 M. 



The following species of Echinoids are known from this region: 



