298 Th. Mortensen. 



Ian tic, boreal species, 3) species belonging to the North- 

 ern Sea, and — perhaps — 4) spe ci es .deri ved from the 

 Northern Pacific. 



The endemic species are Asterias polaris and Ophioglypha 

 Stiiwitzii, which are hitherto known only from the coasts of the 

 Davis Strait, and which must be supposed to have originated in these 

 waters. It is true that Ast. polaris is supposed by Oster gren to have 

 been derived from the Bering Sea; but so long as it is not proved 

 to be identical with A. camtschatica or another Pacific species, we 

 must take it as having developed in the Sea to the West of Greenland. 



The Atlantic boreal fauna is represented by Asterias Miil- 

 leri, Solaster endeca and Psolus phantapus, to which must be added 

 of those species occurring round the whole Coast of Greenland: 

 Solaster papposus, Cribrella sanguinolenta, Ophioglypha Sarsi, Ophia- 

 cantha bidentata and Phyllophorus pellucidus. These species are 

 eurytherm enough to be able to thrive in the littoral region of 

 Greenland, while those named above as Atlantic archibenthal forms 

 are less eurytherm, so that they do not appear to be able to endure 

 the cold of the Polar water. Those occurring also at the East Coast 

 are evidently the most eurytherm, as they can endure the highly 

 arctic conditions of this coast. 



The third group of species, those belonging to the 

 Northern Sea, is the most important. It includes the species: 

 Solaster glacialis, S. squamatus, Pteraster puluillus, Pt. obscurus, Poranio- 

 morpha tumida, Pedicellaster palœocrystalliis, Asterias panopla and A. 

 Linkii. To these may be added of the species occurring (or supposed 

 to occur) round the whole Greenland Coast: Asterias grønlandica, 

 Stichaster albiilus, Solaster furcifer, Ophiocten sericeum, Ophioscolex 

 glacialis, Gorgonocephaliis eucnemis and G. Agassizii. They appear to 

 have first reached the East Coast of Greenland and from there 

 partly spread northwards or southwards (or both) along the coast, 

 some of the latter reaching to the American Coast. 



The group of species which may be supposed to have 

 come from the Arctic Pacific contains the species: Ophioglypha 

 nodosa, Chirodota lœvis, Cucumaria calcigera and Psolus Fabricii, to 

 which may probably be added some more widely distributed species: 

 Strongylocentrotiis drobachiensis, Heliometra glacialis, Pteraster milita- 

 ris, Myriotrochus Rinkii, Phyllophorus pellucidus, Cucumaria frondosaJ 



' According to Ch. L. Edwards (Revision of the Holothurioidea. I. Cucumaria 

 frondosa (Gunner) 1767, and Four species of Pacific Ocean Holothurians allied 

 to Cucumaria frondosa Gunner), Zool. Jahrb. Abt. f. Syst. Bd. 29. 1910), Cue. 

 frondosa does not occur in the Pacific. — These two important papers were 

 received too late to be taken into account in the systematic part of this paper. 



