Report on the Echinoderms of North-East Greenland. 2'.)9 



It seems probable that these species have wandered towards the 

 East from the Pacific. This may be concluded from the fact that 

 f. i. Strongylocentrotiis drøbachiensis does not appear to iiave spread 

 as yet to tlie Eastern Siberian Sea. 



It is a very remarkable fact that so great a number of these 

 species do not appear to have reached down along the East Coast 

 of Greenland (Comp. p. 295). (— It can scarcely be supposed that they 

 altogether have been overlooked there — ). A reasonable explanation 

 of this peculiar fact is difficult to find. In the development of these 

 species it can scarcely be found (viz. in the presence or lacking of 

 pelagic larvæ), since both forms with pelagic larvæ (Strong, drø- 

 bachiensis) and without such {Pteraster militaris) have found their 

 way down along the East Coast. That the climatic conditions are 

 too severe seems scarcely probable. 



One thing is still worth noticing, viz. the absence of a few 

 characteristic species: Echinarachniiis parma, Molpadia borealis and 

 Cucnmaria glacialis. The latter is distributed from Spitzbergen to 

 the Siberian Sea, at least to 172° E. It seems very remarkable that 

 it has not reached Greenland along with the other species endemic 

 in the Northern Sea; the same holds good for Molpadia borealis, 

 which has nearly the same distribution. 



The distribution of Echinarachnius parma is, however, more 

 remarkable. It occurs in the Northern Pacific down to Vancouver 

 Island, and along the Atlantic Coast of North America from Maine 

 to Maryland. From the North Coast of America it is not known. 

 The same appears to be the distribution of Molpadia oölitica. This 

 distribution has probably been brought about through climatic 

 oscillations. In a warmer period, such as has been proved by Ad. 

 S. Jensen to have existed here (when Zirphœa crispata lived at 

 the Greenland Coast) \ they have probably been distributed along 

 the whole of the American North Coast. When the temperature 

 again lowered they disappeared from the northern regions, getting 

 thus their recent discontinuous distribution. It would not seem 

 improbable that they had at that time also reached the Greenland 

 West Coast; there has, however, not hitherto been found remnants 

 of Echinarachnius in the layers containing Zirphœa crispata. — At 

 that warmer period the Atlantic species now only found in the 

 archibenthal region have doubtless occurred much more littoral. 



' Ad. S. Jensen. On the Molkisca of East Greenland. 1. Lamellibranchiata. With 

 an Introduction on Greenlands Mollusc-Fauna from the quaternarj' time. Medd. 

 om Grønland, XXIX. 1905. — Ad. S. Jensen & Foul Harder. Postglacial 

 Changes of climate in arctic regions as revealed by investigations on marine 

 deposits. (Postglaziale Kliniaveränderungen. Stockholm. 1910). 



