ECHINOIDEA. II. 



187 



not have been overlooked in the regions, from where they are hitherto not recorded. It seems then 

 really to be the case, that also the Atlantic deep sea comprises several distinct regions, though it seems 

 impossible for the present to point out special physical characters, which distinguish the separate re- 

 gion.s. As seen in Gerh. Schott's adniiralilc sOceanographie und maritime Meteorologies' the bottom 

 temperature is in the whole Atlantic,' in depths beyond 1000 M., over 2°. Only in the Davis vStrait 

 and in the large Brazilian basin to the West of the midatlantic ridge (from near St. Paul down to the 

 antarctic sea) the temperature is below 2°. But this difference in the temperature does uot seem to 

 be sufficient to cause corresponding marked differences in the deep-sea Echinoid-fauna. 



The subdivision of the deep-sea regions into an archibenthal and abyssal zone is upon the whole 

 not supported by the bathymetrical distribution of the species; most of the species occurring in the 

 abyssal zone also occur in the archibenthal zone, and probably several of the species hitherto not 

 known beyond the archibenthal zone will ultimately prove to have a greater bathymetrical distribution. 

 Still it is worth noticing that the Meridosternata almost exclusively belong to the abyssal zone. 



The European Atlantic deep-sea region comprises the Northern Atlantic, to the East of a 

 line from the Denmark Strait to the Gibraltar Strait.^ It is limited from the cold area of the Nor- 

 wegian Sea by the ridges across the Denmark-vStrait, the Faroe-Channel and between Iceland and the 

 Faroe Islands. 



The following species are known from this region : 



Trigonocidaris albida 

 H\i3siechinus corouatus 

 Echinus esculentus 



— acutus 



— elegans 



— Alexandri 

 affinis 



StrongN'locentrotus drobachiensis Spatangus purpureus 

 Sphserechinus granularis — Raschi 



Echinocyamus pusillus Echinocardium flavescens 



Neolampas rostellata Brissopsis lyrifera. 



Of these species we may first eliminate the following as occasional intruders from the boreal 

 and Mediterranean regions: Ecliinus csculcutus, Strongyloccntrohts drobachiensis, Spharechinus grami- 

 laris and Echinocardium flavescens. Of the rest the following are known from this region only: Arce- 

 osoma violaceum, Echinosoma iiranus, Hypsiechinus coronatus, Plexechinus hirstihis, Echinosigra (Pour- 

 talesia) phiale and paradoxa. Porocidaris piirpiirata and Sperosonia Grivialdi are known only from this 

 and the West African region. These species are, however, (except Porocidaris purpurata and Spero- 

 sonia Grinialdi) either small or easily confused with other species. It is certainly not much to 

 characterize the region by, but especially Porocidaris purpurata and Sperosonia Grimaldi are so mag- 

 nificent and peculiar forms that the\- can certainly not have been confused with other species; the 



Dorocidaris papillata 

 Stereocidaris ingolfiana 

 Porocidaris purpurata 

 Phormosoma placenta 

 Calveria hystrix 

 Arseosoma fenestratum 



— violaceum 



Hygrosoma Petersi 

 Sperosonia Grimaldi 

 Echinosoma uranus 

 Salenia hastigera 



Urechinus naresianus 

 Plexechinus hirsutus 

 Pourtalesia Wandeli 

 Echinosigra (Pourtalesia) phiale 



— — paradoxa 



Hemiaster expergitus 

 Brisaster frag-ilis 



1 Wissensch. Ergebn. d. deutsch. Tiefsee-Exp. I. 1902. 



2 The limit between the European and the East American Atlantic deep-sea regions will undoubtedly prove not to 

 be a straight line of the course here indicated. For the present, however, our knowledge of the deep-sea fauna of the Mid- 

 Atlautic is too insufficient for pointing out the Umit between these regions more exactly. 



